Picture coding device, picture coding method, picture coding program

ABSTRACT

In a case where a partition mode in which luma signals are partitioned horizontally and vertically is set when an intra prediction of a picture signal is made in units of minimal coding blocks set in advance, an intra prediction unit is configured to make an intra prediction of a chroma signal in units of prediction blocks of the intra prediction of chroma signals within the minimal coding block set in accordance with a chroma format. A second bitstream constructing unit constructs a bitstream of information relating to a luma intra prediction mode of a prediction block of luma signals and information relating to a chroma intra prediction mode of a prediction block of chroma signals.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.15/966,033 filed on Apr. 30, 2018; which is a Continuation of U.S.patent application Ser. No. 15/145,520, filed May 3, 2016, now U.S. Pat.No. 10,009,607; which is a Continuation of U.S. patent application Ser.No. 14/563,544 filed on Dec. 8, 2014; now U.S. Pat. No. 9,363,521; whichis a Continuation of U.S. patent application Ser. No. 14/135,253 filedon Dec. 19, 2013, now U.S. Pat. No. 8,938,003; which is a Continuationof PCT International Application No. PCT/JP2012/003887 filed on Jun. 14,2012, which claims the benefit of Japanese Patent Application Nos.2011-139677 and 2011-139678 filed on Jun. 23, 2011, all of which areincorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a picture coding and decodingtechnology, and more particularly, to an intra coding and decodingtechnology.

As a representative compression coding mode of moving pictures, there isan MPEG-4 AVC/H.264 standard. According to MPEG-4 AVC/H.264, coding isperformed in units of macroblocks acquired by partitioning a pictureinto a plurality of rectangular blocks. The size of the macroblock isdefined as 16.times.16 pixels in a luma signal regardless of the picturesize. While a chroma signal is also included in the macroblock, the sizeof the chroma signal included in the macroblock differs in accordancewith a chroma format of a picture to be coded. Thus, in a case where thechroma format is 4:2:0, the size of the chroma signal is 8.times.8pixels, in a case where the chroma format is 4:2:2, the size of thechroma signal is 8.times.16 pixels, and, in a case where the chromaformat is 4:4:4, the size of the chroma signal is 16.times.16 pixels.

As the chroma format, the ratio of sampled pixel numbers of threesignals of one luma information unit and two chroma information units isdenoted by X:Y:Z. As the chroma formats of a picture that is a targetfor being coded and decoded in accordance with MPEG-4 AVC/H.264, thereare 4:2:0, 4:2:2, 4:4:4, and monochrome.

FIGS. 3A to 3E are diagrams that illustrate the chroma formats of apicture. In the figures, “x” denotes the position of a pixel of a lumasignal on the plane of the screen, and “.largecircle.” denotes theposition of a pixel of a chroma signal.

The chroma format of 4:2:0 illustrated in FIG. 3A is a chroma format inwhich chroma signals are sampled in both horizontal and verticaldirections at a half density with respect to luma signals. In addition,in the chroma format of 4:2:0, chroma signals may be sampled atpositions illustrated in FIG. 3E.

The chroma format of 4:2:2 illustrated in FIG. 3B is a chroma format inwhich chroma signals are sampled in the horizontal direction at a halfdensity, and in the vertical direction at the same density with respectto luma signals.

The chroma format of 4:4:4 illustrated in FIG. 3C is a chroma format inwhich chroma signals and luma signals are sampled at the same density.

The chroma format of monochrome illustrated in FIG. 3D is a chromaformat that is configured only by luma signals without any chromasignal.

While the luma signals and the chroma signals are set so as to sharecoding information such as motion compensation and are coded anddecoded, in the chroma format of 4:4:4, a structure is also provided inwhich one luma signal and two chroma signals are independently coded anddecoded as three monochrome signals.

In the AVC/H.264 mode, a technique is used in which a prediction is madebased on coded/decoded blocks within the coding/decoding target pixel.Such a technique is called an intra prediction. In addition, motioncompensation is used in which a coded/decoded picture is set as areference picture, and a motion from the reference picture is predicted.A technique for predicting a motion based on the motion compensation iscalled an inter prediction.

First, in an intra prediction made in intra coding according to theAVC/H.264 mode, units in which switching between intra prediction modesis performed will be described. FIGS. 4A to 4C are diagrams thatillustrate the units in which switching between intra prediction modesis performed. In intra coding according to the AVC/H.264 mode, as theunits in which switching between intra prediction modes is performed,three types including a “4.times.4 intra prediction”, a “16.times.16intra prediction”, and an “8.times.8 intra prediction” are prepared.

In the “4.times.4 intra prediction”, luma signals of a macroblock (aluma signal 16.times.16 pixel block and a chroma signal 8.times.8 pixelblock) are partitioned into 16 4.times.4 pixel blocks, a mode isselected from among 9 types of 4.times.4 intra prediction modes in unitsof the partitioned 4.times.4 pixels, and intra predictions aresequentially made (FIG. 4A).

In the “16.times.16 intra prediction”, a mode is selected from among 4types of 16.times.16 intra prediction modes in units of 16.times.16pixel blocks of luma signals, and intra predictions are made (FIG. 4B).

In the “8.times.8 intra prediction”, luma signals of a macroblock arepartitioned into 4 8.times.8 pixel blocks, a mode is selected from among9 types of 8.times.8 intra prediction modes in units of the partitioned8.times.8 pixels, and intra predictions are sequentially made (FIG. 4C).

In addition, in intra predictions of chroma signals, in a case where thechroma format is 4:2:0 or 4:2:2, a mode is selected from among 4 typesof intra prediction modes of chroma signals in units of macroblocks, andthe intra predictions are made.

Next, units in which an inter prediction is made in inter codingaccording to the AVC/H.264 mode will be described. FIGS. 5A to 5H arediagrams that illustrate macroblock partitions and sub-macroblockpartitions. Here, for the simplification of description, only pixelblocks of luma signals are illustrated. In the MPEG series, a macroblockis defined as a square area. Generally, in the MPEG series including theAVC/H.264 mode, a block that is defined as 16.times.16 pixels (16horizontal pixels and 16 vertical pixels) is called a macroblock. Inaddition, in the AVC/H.264 mode, a block that is defined as 8.times.8pixels is called a sub-macroblock. A macroblock partition represents asmall block acquired by further partitioning the macroblock for a motioncompensation prediction. A sub-macroblock partition represents a smallblock acquired by further partitioning the sub-macroblock for a motioncompensation prediction.

FIG. 5A is a diagram illustrating that a macroblock is configured by onemacroblock partition that is configured by luma signals of 16.times.16pixels and two chroma signals corresponding thereto. Here, such aconfiguration will be referred to as a macroblock type of a 16.times.16mode.

FIG. 5B is a diagram illustrating that a macroblock is configured by twomacroblock partitions each being configured by luma signals of16.times.8 pixels (horizontal 16 pixels and vertical 8 pixels) and twochroma signals corresponding thereto. These two macroblock partitionsare vertically aligned. Here, such a configuration will be referred toas a macroblock type of a 16.times.8 mode.

FIG. 5C is a diagram illustrating that a macroblock is configured by twomacroblock partitions each being configured by luma signals of8.times.16 pixels (horizontal 8 pixels and vertical 16 pixels) and twochroma signals corresponding thereto. These two macroblock partitionsare horizontally aligned. Here, such a configuration will be referred toas a macroblock type of an 8.times.16 mode.

FIG. 5D is a diagram illustrating that a macroblock is configured byfour macroblock partitions each being configured by luma signals of8.times.8 pixels and two chroma signals corresponding thereto. Each twoof these four macroblock partitions are aligned vertically andhorizontally. Here, such a configuration will be referred to as amacroblock type of an 8.times.8 mode.

FIG. 5E is a diagram illustrating that a sub-macroblock is configured byone sub-macroblock partition that is configured by luma signals of8.times.8 pixels and two chroma signals corresponding thereto. Here,such a configuration will be referred to as a sub-macroblock type of the8.times.8 mode.

FIG. 5F is a diagram illustrating that a sub-macroblock is configured bytwo sub-macroblock partitions each being configured by luma signals of8.times.4 pixels (horizontal 8 pixels and vertical 4 pixels) and twochroma signals corresponding thereto. These two sub-macroblockpartitions are vertically aligned. Here, such a configuration will bereferred to as a sub-macroblock type of an 8.times.4 mode.

FIG. 5G is a diagram illustrating that a sub-macroblock is configured bytwo sub-macroblock partitions each being configured by luma signals of4.times.8 pixels (horizontal 4 pixels and vertical 8 pixels) and twochroma signals corresponding thereto. These two sub-macroblockpartitions are horizontally aligned. Here, such a configuration will bereferred to as a sub-macroblock type of a 4.times.8 mode.

FIG. 5H is a diagram illustrating that a sub-macroblock is configured byfour sub-macroblock partitions each being configured by luma signals of4.times.4 pixels and two chroma signals corresponding thereto. Each twoof these four sub-macroblock partitions are aligned vertically andhorizontally. Here, such a configuration will be referred to as asub-macroblock type of a 4.times.4 mode.

In the AVC/H.264 coding mode, a structure is employed in which any oneof the above-described motion compensation block sizes can be selectedand used. First, as the motion compensation block size in the unit of amacroblock, any one of macroblock types of the 16.times.16, 16.times.8,8.times.16, and 8.times.8 modes may be selected. In a case where themacroblock type of the 8.times.8 mode is selected, as the motioncompensation block size in the unit of a sub-macroblock, any one of thesub-macroblock types of the 8.times.8, 8.times.4, 4.times.8, and4.times.4 modes may be selected.

-   Non-Patent Document 1: ISO/IEC 14496-10 Information    technology—Coding of audio-visual objects—Part 10: Advanced Video    Coding is an example of related art.

When information relating to the intra prediction mode of a picturesignal is coded, information relating to the intra prediction mode ofluma signals and information relating to the intra prediction mode ofchroma signals are coded and are arranged within a bitstream, and, atthat time, in a case where the intra prediction mode is not coded inaccordance with the chroma format, the processing efficiency may bedegraded.

SUMMARY OF THE INVENTION

The present invention is contrived in consideration of such situations,and an object thereof is to provide a picture coding and decodingtechnology capable of coding a picture signal with high efficiency byperforming intra predictions of a luma signal and a chroma signal inaccordance with the chroma format.

In order to solve the above problem, a picture coding device accordingto an aspect of the present invention performs intra prediction codingof a picture signal including a luma signal and a chroma signal in unitsof blocks and codes information relating to an intra prediction mode.The picture coding device includes: a luma signal intra prediction unit(103) configured to set the first to fourth prediction blocks of lumasignals acquired by partitioning the luma signals of a minimal codingblock horizontally and vertically and predict a luma signal based on acoded neighboring block of the luma signals in accordance with a lumaintra prediction mode for each prediction block of the luma signals in acase where a partition mode in which the luma signals are partitionedhorizontally and vertically is set when an intra prediction of thepicture signal is made in units of minimal coding blocks set in advance;a chroma signal intra prediction unit (103) configured to set aprediction block of the chroma signals without partitioning the chromasignals of the minimal coding block and predict a chroma signal based ona coded neighboring block of the chroma signals in accordance with achroma intra prediction mode in a case where the partition mode is set,and a chroma format is 4:2:0; and a bitstream constructing unit (113)configured to code information relating to the prediction mode of theminimal coding block and construct a bitstream in which informationrelating to prediction modes is arranged in order of, within the minimalcoding block, the luma intra prediction mode of the first predictionblock of luma signals, the luma intra prediction mode of the secondprediction block of luma signals, the luma intra prediction mode of thethird prediction block of luma signals, the luma intra prediction modeof the fourth prediction block of luma signals, and the chroma intraprediction mode of the prediction block of the chroma signals that islocated at a reference position that is the same as the position of thefirst prediction block of luma signals.

According to another aspect of the present invention, there is alsoprovided a picture coding device that performs intra prediction codingof a picture signal including a luma signal and a chroma signal in unitsof blocks and codes information relating to an intra prediction mode,and the picture coding device includes: a luma signal intra predictionunit (103) that, when an intra prediction of the picture signal is madein units of minimal coding blocks set in advance, in a case where apartition mode in which luma signals are partitioned horizontally andvertically is set, sets the first to fourth prediction blocks of lumasignals acquired by partitioning the luma signals of a minimal codingblock horizontally and vertically and predicts a luma signal based on acoded neighboring block of the luma signals in accordance with a lumaintra prediction mode for each prediction block of the luma signals; achroma signal intra prediction unit (103) that, in a case where thepartition mode is set, and a chroma format is 4:4:4, sets the first tofourth prediction blocks of chroma signals acquired by partitioning thechroma signals of the minimal coding block horizontally and verticallyand predicts the chroma signal based on a coded neighboring block of thechroma signals in accordance with a chroma intra prediction mode foreach prediction block of the chroma signals; and a bitstreamconstructing unit (113) that codes information relating to theprediction mode of the minimal coding block and constructs a bitstreamin which information relating to the prediction modes is arranged inorder of, within the minimal coding block, the luma intra predictionmode of the first prediction block of luma signals, the luma intraprediction mode of the second prediction block of luma signals, the lumaintra prediction mode of the third prediction block of luma signals, theluma intra prediction mode of the fourth prediction block of lumasignals, the chroma intra prediction mode of the prediction block of thefirst chroma signals located at a reference position that is the same asthe position of the first prediction block of luma signals, the chromaintra prediction mode of the prediction block of the second chromasignals located at a reference position that is the same as the positionof the second prediction block of luma signals, the chroma intraprediction mode of the prediction block of the third chroma signalslocated at a reference position that is the same as the position of thethird prediction block of luma signals, and the chroma intra predictionmode of the prediction block of the fourth chroma signals located at areference position that is the same as the position of the fourthprediction block of luma signals.

According to further another aspect of the present invention, there isalso provided a picture coding device that performs intra predictioncoding of a picture signal including a luma signal and a chroma signalin units of blocks and codes information relating to an intra predictionmode, and the picture coding device includes: a luma signal intraprediction unit (103) that, when an intra prediction of the picturesignal is made in units of minimal coding blocks set in advance, in acase where a partition mode in which luma signals are partitionedhorizontally and vertically is set, sets the first to fourth predictionblocks of luma signals acquired by partitioning the luma signals of aminimal coding block horizontally and vertically and predicts a lumasignal based on a coded neighboring block of the luma signals inaccordance with a luma intra prediction mode for each prediction blockof the luma signals; a chroma signal intra prediction unit (103) that,in a case where the partition mode is set, and a chroma format is 4:2:2,sets prediction blocks of first and second chroma signals acquired byhorizontally partitioning the chroma signals of the minimal coding blockand predicts the chroma signal based on a coded neighboring block ofchroma signals in accordance with a chroma intra prediction mode foreach prediction block of the chroma signals; and a bitstreamconstructing unit (113) that codes information relating to theprediction mode of the minimal coding block and constructs a bitstreamin which information relating to the prediction modes is arranged inorder of, within the minimal coding block, the luma intra predictionmode of the first prediction block of luma signals, the luma intraprediction mode of the second prediction block of luma signals, the lumaintra prediction mode of the third prediction block of luma signals, theluma intra prediction mode of the fourth prediction block of lumasignals, the chroma intra prediction mode of the prediction block of thefirst chroma signals located at a reference position that is the same asthe position of the prediction block of the first luma signal, and thechroma intra prediction mode of the prediction block of the secondchroma signals located at a reference position that is the same as theposition of the third prediction block of luma signals.

According to further another aspect of the present invention, there isprovided a picture coding method for performing intra prediction codingof a picture signal including a luma signal and a chroma signal in unitsof blocks and coding information relating to an intra prediction mode,and the picture coding method includes: setting the first to fourthprediction blocks of luma signals acquired by partitioning the lumasignals of a minimal coding block horizontally and vertically andpredicting a luma signal based on a coded neighboring block of the lumasignals in accordance with a luma intra prediction mode for eachprediction block of the luma signals when an intra prediction of thepicture signal is made in units of minimal coding blocks set in advance,in a case where a partition mode in which the luma signals arepartitioned horizontally and vertically is set; setting a predictionblock of chroma signals without partitioning the chroma signals of theminimal coding block and predicting a chroma signal based on a codedneighboring block of the chroma signals in accordance with a chromaintra prediction mode in a case where the partition mode is set, and achroma format is 4:2:0; and coding information relating to theprediction mode of the minimal coding block and constructing a bitstreamin which information relating to the prediction modes is arranged inorder of, within the minimal coding block, the luma intra predictionmode of the first prediction block of luma signals, the luma intraprediction mode of the second prediction block of luma signals, the lumaintra prediction mode of the third prediction block of luma signals, theluma intra prediction mode of the fourth prediction block of lumasignals, and the chroma intra prediction mode of the prediction block ofthe chroma signals located at a reference position that is the same asthe position of the first prediction block of luma signals.

According to further another aspect of the present invention, there isalso provided a picture coding method for performing intra predictioncoding of a picture signal including a luma signal and a chroma signalin units of blocks and coding information relating to an intraprediction mode, and the picture coding method includes: setting thefirst to fourth prediction blocks of luma signals acquired bypartitioning the luma signals of a minimal coding block horizontally andvertically and predicting a luma signal based on a coded neighboringblock of the luma signals in accordance with a luma intra predictionmode for each prediction block of the luma signals when an intraprediction of the picture signal is made in units of the minimal codingblocks set in advance, in a case where a partition mode in which theluma signals are partitioned horizontally and vertically is set; settingthe first to fourth prediction blocks of chroma signals acquired bypartitioning the chroma signals of the minimal coding block horizontallyand vertically and predicting a chroma signal based on a codedneighboring block of the chroma signals in accordance with a chromaintra prediction mode for each prediction block of the chroma signals ina case where the partition mode is set, and a chroma format is 4:4:4;and coding information relating to the prediction mode of the minimalcoding block and constructing a bitstream in which information relatingto the prediction modes is arranged in order of, within the minimalcoding block, the luma intra prediction mode of the first predictionblock of luma signals, the luma intra prediction mode of the secondprediction block of luma signals, the luma intra prediction mode of thethird prediction block of luma signals, the luma intra prediction modeof the fourth prediction block of luma signals, the chroma intraprediction mode of the prediction block of the first chroma signalslocated at a reference position that is the same as the position of thefirst prediction block of luma signals, the chroma intra prediction modeof the prediction block of the second chroma signals located at areference position that is the same as the position of the secondprediction block of luma signals, the chroma intra prediction mode ofthe prediction block of the third chroma signals located at a referenceposition that is the same as the position of the third prediction blockof luma signals, and the chroma intra prediction mode of the predictionblock of the fourth chroma signals located at a reference position thatis the same as the position of the fourth prediction block of lumasignals.

According to further another aspect of the present invention, there isprovided a picture coding method for performing intra prediction codingof a picture signal including a luma signal and a chroma signal in unitsof blocks and coding information relating to an intra prediction mode,and the picture coding method includes: setting the first to fourthprediction blocks of luma signals acquired by partitioning the lumasignals of a minimal coding block horizontally and vertically andpredicting a luma signal based on a coded neighboring block of the lumasignals in accordance with a luma intra prediction mode for eachprediction block of the luma signals when an intra prediction of thepicture signal is made in units of the minimal coding blocks set inadvance, in a case where a partition mode in which the luma signals arepartitioned horizontally and vertically is set; setting predictionblocks of first and second chroma signals acquired by horizontallypartitioning the chroma signals of the minimal coding block andpredicting a chroma signal based on a coded neighboring block of thechroma signals in accordance with a chroma intra prediction mode foreach prediction block of the chroma signals in a case where thepartition mode is set, and a chroma format is 4:2:2; and codinginformation relating to the prediction mode of the minimal coding blockand constructing a bitstream in which information relating to theprediction modes is arranged in order of, within the minimal codingblock, the luma intra prediction mode of the first prediction block ofluma signals, the luma intra prediction mode of the second predictionblock of luma signals, the luma intra prediction mode of the thirdprediction block of luma signals, the luma intra prediction mode of thefourth prediction block of luma signals, the chroma intra predictionmode of the prediction block of the first chroma signals located at areference position that is the same as the position of the predictionblock of the first luma signal, and the chroma intra prediction mode ofthe prediction block of the second chroma signals located at a referenceposition that is the same as the position of the third prediction blockof luma signals.

A picture decoding device according to an aspect of the presentinvention decodes information relating to an intra prediction mode andperforms intra prediction decoding of a picture signal including a lumasignal and a chroma signal in units of blocks, and the picture decodingdevice includes: a bitstream decoding unit (203) configured to decodeinformation relating to a luma intra prediction mode of a predictionblock of luma signals and information relating to a chroma intraprediction mode of the prediction block of chroma signals in the orderof arrangement from a bitstream in which coding information relating tothe prediction mode is arranged in order of, within a minimal decodingblock, a luma intra prediction mode of the first prediction block ofluma signals, a luma intra prediction mode of the second predictionblock of luma signals, a luma intra prediction mode of the thirdprediction block of luma signals, a luma intra prediction mode of thefourth prediction block of luma signals, and a chroma intra predictionmode of the prediction block of the chroma signals that is located at areference position that is the same as the position of the firstprediction block of luma signals, in a case where a partition mode inwhich the luma signals are partitioned horizontally and vertically isderived and a chroma format is 4:2:0 when an intra prediction of thepicture signal is made in units of minimal decoding blocks set inadvance; a luma signal intra prediction unit (206) that, in a case wherethe partition mode is set, is configured to set the first to fourthprediction blocks of luma signals acquired by partitioning the lumasignals of the minimal decoding block horizontally and vertically andpredict a luma signal based on a decoded neighboring block of the lumasignals in accordance with each luma intra prediction mode derived basedon the information relating to the luma intra prediction mode for eachdecoded prediction block of the luma signals; and a chroma signal intraprediction unit (206) configured to set the prediction block of thechroma signals without partitioning the chroma signals of the minimaldecoding block and predict a chroma signal based on a decodedneighboring block of the chroma signals in accordance with a chromaintra prediction mode derived based on the information relating to thedecoded chroma intra prediction mode in a case where the partition modeis set, and the chroma format is 4:2:0.

According to another aspect of the present invention, there is alsoprovided a picture decoding device that decodes information relating toan intra prediction mode and performs intra prediction decoding of apicture signal including a luma signal and a chroma signal in units ofblocks, and the picture decoding device includes: a bitstream decodingunit (203) that decodes information relating to a luma intra predictionmode of the prediction block of luma signals and information relating toa chroma intra prediction mode of the prediction block of chroma signalsin the order of arrangement from a bitstream in which coding informationrelating to the prediction mode is arranged in order of, within theminimal decoding block, a luma intra prediction mode of the firstprediction block of luma signals, a luma intra prediction mode of thesecond prediction block of luma signals, a luma intra prediction mode ofthe third prediction block of luma signals, a luma intra prediction modeof the fourth prediction block of luma signals, a chroma intraprediction mode of the prediction block of the first chroma signalslocated at a reference position that is the same as the position of thefirst prediction block of luma signals, a chroma intra prediction modeof the prediction block of the second chroma signals located at areference position that is the same as the position of the secondprediction block of luma signals, a chroma intra prediction mode of theprediction block of the third chroma signals located at a referenceposition that is the same as the position of the third prediction blockof luma signals, and a chroma intra prediction mode of the predictionblock of the fourth chroma signals located at a reference position thatis the same as the position of the fourth prediction block of lumasignals, in a case where a partition mode in which the luma signals arepartitioned horizontally and vertically is derived, and a chroma formatis 4:4:4 when an intra prediction of a picture signal is made in unitsof minimal decoding blocks set in advance; a luma signal intraprediction unit (206) that sets the first to fourth prediction blocks ofluma signals acquired by partitioning the luma signals of the minimaldecoding block horizontally and vertically and predicts the luma signalbased on the decoded neighboring block of luma signals in accordancewith each luma intra prediction mode derived based on the informationrelating to the luma intra prediction mode for each decoded predictionblock of the luma signals in a case where the partition mode is set; anda chroma signal intra prediction unit (206) that sets the first tofourth prediction blocks of chroma signals that are acquired bypartitioning the chroma signals of the minimal decoding blockhorizontally and vertically and predicts the chroma signal based on adecoded neighboring block of chroma signals in accordance with a chromaintra prediction mode derived based on the information relating to thechroma intra prediction mode for each decoded prediction block of thechroma signals in a case where the partition mode is set, and the chromaformat is 4:4:4.

According to further another aspect of the present invention, there isalso provided a picture decoding device that decodes informationrelating to an intra prediction mode and performs intra predictiondecoding of a picture signal including a luma signal and a chroma signalin units of blocks, and the picture decoding device includes: abitstream decoding unit (203) that decodes information relating to aluma intra prediction mode of the prediction block of luma signals andinformation relating to a chroma intra prediction mode of the predictionblock of chroma signals in order of arrangement from a bitstream inwhich coding information relating to the prediction mode is arranged inthe order of, within the minimal decoding block, the luma intraprediction mode of the first prediction block of luma signals, the lumaintra prediction mode of the second prediction block of luma signals,the luma intra prediction mode of the third prediction block of lumasignals, the luma intra prediction mode of the fourth prediction blockof luma signals, the chroma intra prediction mode of the predictionblock of the first chroma signals located at a reference position thatis the same as the position of the prediction block of the first lumasignal, and the chroma intra prediction mode of the prediction block ofthe second chroma signals located at a reference position that is thesame as the position of the third prediction block of luma signals in acase where a partition mode in which the luma signals are horizontallyand vertically partitioned is derived, and a chroma format is 4:2:2 whenan intra prediction of a picture signal is made in units of minimaldecoding blocks set in advance; a luma signal intra prediction unit(206) that, in a case where the partition mode is set, sets the first tofourth prediction blocks of luma signals acquired by partitioning theluma signals of the minimal decoding block horizontally and verticallyand predicts the luma signal based on the decoded neighboring block ofluma signals in accordance with each luma intra prediction mode derivedbased on the information relating to the luma intra prediction mode foreach decoded prediction block of the luma signals; and a chroma signalintra prediction unit (206) that, in a case where the partition mode isset, and the chroma format is 4:2:2, sets prediction blocks of first andsecond chroma signals that are acquired by horizontally partitioning thechroma signals of the minimal decoding block and predicts the chromasignal based on a decoded neighboring block of chroma signals inaccordance with a chroma intra prediction mode derived based on theinformation relating to the chroma intra prediction mode for eachdecoded prediction block of the chroma signals.

According to further another aspect of the present invention, there isalso provided a picture decoding method for decoding informationrelating to an intra prediction mode and performing intra predictiondecoding of a picture signal including a luma signal and a chroma signalin units of blocks, and the picture decoding method includes: decodinginformation relating to a luma intra prediction mode of the predictionblock of luma signals and information relating to a chroma intraprediction mode of the prediction block of chroma signals in the orderof arrangement from a bitstream in which coding information relating tothe prediction mode is arranged in order of, within the minimal decodingblock, a luma intra prediction mode of the first prediction block ofluma signals, a luma intra prediction mode of the second predictionblock of luma signals, a luma intra prediction mode of the thirdprediction block of luma signals, a luma intra prediction mode of thefourth prediction block of luma signals, and a chroma intra predictionmode of the prediction block of the chroma signals that is located at areference position that is the same as the position of the firstprediction block of luma signals in a case where a partition mode inwhich the luma signals are partitioned horizontally and vertically isderived and a chroma format is 4:2:0 when an intra prediction of apicture signal is made in units of minimal decoding blocks set inadvance; setting the first to fourth prediction blocks of luma signalsacquired by partitioning the luma signals of the minimal decoding blockhorizontally and vertically and predicting a luma signal based on adecoded neighboring block of the luma signals in accordance with eachluma intra prediction mode derived based on the information relating tothe luma intra prediction mode for each decoded prediction block of theluma signals in a case where the partition mode is set; and setting theprediction block of the chroma signals without partitioning the chromasignals of the minimal decoding block and predicting a chroma signalbased on a decoded neighboring block of the chroma signals in accordancewith a chroma intra prediction mode derived based on the informationrelating to the decoded chroma intra prediction mode in a case where thepartition mode is set, and the chroma format is 4:2:0.

According to further another aspect of the present invention, there isalso provided a picture decoding method for decoding informationrelating to an intra prediction mode and performing intra predictiondecoding of a picture signal including a luma signal and a chroma signalin units of blocks, and the picture decoding method includes: decodinginformation relating to a luma intra prediction mode of a predictionblock of the luma signals and information relating to a chroma intraprediction mode of the prediction block of the chroma signals in theorder of arrangement from a bitstream in which coding informationrelating to a prediction mode is arranged in order of, within a minimaldecoding block, a luma intra prediction mode of a prediction block offirst luma signals, a luma intra prediction mode of a prediction blockof second luma signals, a luma intra prediction mode of a predictionblock of third luma signals, a luma intra prediction mode of aprediction block of fourth luma signals, a chroma intra prediction modeof a prediction block of first chroma signals located at a referenceposition that is the same as the position of the first prediction blockof luma signals, a chroma intra prediction mode of a prediction block ofsecond chroma signals located at a reference position that is the sameas the position of the second prediction block of luma signals, a chromaintra prediction mode of a prediction block of third chroma signalslocated at a reference position that is the same as the position of thethird prediction block of luma signals, and a chroma intra predictionmode of a prediction block of fourth chroma signals located at areference position that is the same as the position of the fourthprediction block of luma signals, in a case where a partition mode inwhich the luma signals are partitioned horizontally and vertically isderived, and a chroma format is 4:4:4 when an intra prediction of thepicture signal is made in units of the minimal decoding blocks set inadvance; setting the first to fourth prediction blocks of luma signalsacquired by partitioning the luma signals of the minimal decoding blockhorizontally and vertically and predicting a luma signal based on adecoded neighboring block of the luma signals in accordance with eachluma intra prediction mode derived based on the information relating tothe luma intra prediction mode for each decoded prediction block of theluma signals in a case where the partition mode is set; and setting thefirst to fourth prediction blocks of chroma signals that are acquired bypartitioning the chroma signals of the minimal decoding blockhorizontally and vertically and predicting a chroma signal based on adecoded neighboring block of the chroma signals in accordance with eachchroma intra prediction mode derived based on the information relatingto the chroma intra prediction mode for each decoded prediction block ofthe chroma signals in a case where the partition mode is set, and thechroma format is 4:4:4.

According to further another aspect of the present invention, there isalso provided a picture decoding method for decoding informationrelating to an intra prediction mode and performing intra predictiondecoding of a picture signal including a luma signal and a chroma signalin units of blocks, and the picture decoding method includes: decodinginformation relating to a luma intra prediction mode of a predictionblock of the luma signals and information relating to a chroma intraprediction mode of a prediction block of the chroma signals in the orderof arrangement from a bitstream in which coding information relating toa prediction mode is arranged in order of, within a minimal decodingblock, the luma intra prediction mode of a prediction block of firstluma signals, the luma intra prediction mode of a prediction block ofsecond luma signals, the luma intra prediction mode of a predictionblock of third luma signals, the luma intra prediction mode of aprediction block of fourth luma signals, the chroma intra predictionmode of a prediction block of first chroma signals located at areference position that is the same as the position of the predictionblock of the first luma signal, and the chroma intra prediction mode ofa prediction block of second chroma signals located at a referenceposition that is the same as the position of the third prediction blockof luma signals in a case where a partition mode in which the lumasignals are partitioned horizontally and vertically is derived, and achroma format is 4:2:2 when an intra prediction of the picture signal ismade in units of the minimal decoding blocks set in advance; setting thefirst to fourth prediction blocks of luma signals acquired bypartitioning the luma signals of the minimal decoding block horizontallyand vertically and predicting a luma signal based on a decodedneighboring block of the luma signals in accordance with each luma intraprediction mode derived based on the information relating to the lumaintra prediction mode for each decoded prediction block of the lumasignals in a case where the partition mode is set; and setting theprediction blocks of the first and second chroma signals that areacquired by horizontally partitioning the chroma signals of the minimaldecoding block and predicting a chroma signal based on a decodedneighboring block of the chroma signals in accordance with each chromaintra prediction mode derived based on the information relating to thechroma intra prediction mode for each decoded prediction block of thechroma signals in a case where the partition mode is set, and the chromaformat is 4:2:2.

In addition, an arbitrary combination of constituent elements describedabove and any conversion of the representation of the present inventionamong a device, a system, a recording medium, a computer program, andthe like are also effective as aspects of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram that illustrates the configuration of apicture coding device according to an embodiment;

FIG. 2 is a block diagram that illustrates the configuration of apicture decoding device according to an embodiment;

FIGS. 3A to 3E are diagrams that illustrate chroma formats of a picture;

FIGS. 4A to 4C are diagrams that illustrate units in which switchingbetween intra prediction modes according to an AVC/H.264 mode isperformed;

FIGS. 5A to 5H are diagrams that illustrate units in which an interprediction according to the AVC/H.264 mode is made;

FIG. 6 is a diagram that illustrates tree blocks and coding blocksdefined in this example;

FIGS. 7A to 7D are diagrams that illustrate partition modes defined inthis example;

FIG. 8 is a diagram that illustrates values of intra prediction modesand prediction directions defined in this example;

FIG. 9 is a diagram that illustrates an example of the positions ofblocks defined in this example;

FIG. 10 is a diagram that illustrates an example of the definition ofsyntax at the time of coding chroma format information using thesequence parameter set that is a header for coding information relatingto coding the entire sequence defined in this example;

FIGS. 11A to 11D are diagrams that illustrate methods of partitioningchroma signals of a coding block for N.times.N partition at the time ofperforming an intra prediction defined in this example;

FIG. 12 is a block diagram that illustrates the configuration of asecond bitstream constructing unit of the picture coding deviceaccording to the embodiment;

FIG. 13 is a block diagram that illustrates the configuration of asecond bitstream decoding unit of the picture decoding device accordingto the embodiment;

FIG. 14 is a conversion table used for calculating the value of a chromaintra prediction mode based on the value of a syntax element used on thedecoding side and the value of a luma intra prediction mode of aprediction block of a luma signal that is located at the same positionas the position of a prediction block of a chroma signal that is definedin this example;

FIG. 15 is a conversion table used for calculating the value of a chromaintra prediction mode based on the value of a luma intra prediction modeof a prediction block located at the same position as the position of aprediction block of chroma signals in a case where the chroma format is4:2:2 that is defined in this example;

FIG. 16 is a conversion table used for calculating the value of a syntaxelement relating to a chroma intra prediction mode based on the value ofa chroma intra prediction mode used on the coding side and the value ofa luma intra prediction mode of a prediction block of luma signals thatis located at the same position as the position of a prediction block ofa chroma signal that is defined in this example;

FIGS. 17A to 17C are diagrams that illustrate entropy coding or decodingsequences of syntax elements relating to a luma intra prediction modeand a chroma intra prediction mode at the time of N.times.N partitionaccording to an embodiment;

FIG. 18 is an example of a syntax rule used for coding and decodingcoding information of a prediction block that is defined in thisexample;

FIG. 19 is another example of a syntax rule, which is different from theexample illustrated in FIG. 18, used for coding and decoding codinginformation of a prediction block that is defined in this example;

FIG. 20 is a flowchart that illustrates the processing sequence of acoding process in units of coding blocks and prediction blocks that isperformed by the second bitstream constructing unit according to theembodiment;

FIG. 21 is a flowchart that illustrates the sequence of a common codingprocess that is used in steps S1003, S1007, S1011, and S1014, which areillustrated in FIG. 20, according to the embodiment;

FIG. 22 is a flowchart that illustrates the sequence of a common codingprocess that is used in steps S1005, S1009, S1013, and S1016, which areillustrated in FIG. 20, according to the embodiment;

FIG. 23 is a flowchart that illustrates the processing sequence of adecoding process in units of coding blocks and prediction blocks that isperformed by the second bitstream decoding unit according to theembodiment;

FIG. 24 is a flowchart that illustrates the sequence of a commondecoding process that is used in steps S2003, S2007, S2010, and S2013,which are illustrated in FIG. 23, according to the embodiment;

FIG. 25 is a flowchart that illustrates the sequence of a commondecoding process that is used in steps S2005, S2009, S2012, and S2015,which are illustrated in FIG. 23, according to the embodiment;

FIG. 26 is a flowchart that illustrates the sequence of the process ofcalculating the value of a chroma intra prediction mode used in stepS2202, which is illustrated in FIG. 25, according to the embodiment;

FIGS. 27A and 27B are diagrams that illustrate the correspondencerelation between the prediction directions of intra predictions of aluma signal and a chroma signal in a case where the chroma format is4:2:2; and

FIGS. 28A and 28B are diagrams that illustrate the correspondencerelation between the prediction directions of intra predictions of aluma signal and a chroma signal in a case where the chroma format is4:2:0.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention will now be described by reference to the preferredembodiments. This does not intend to limit the scope of the presentinvention, but to exemplify the invention.

This embodiment relates to coding a moving picture, and, moreparticularly, in units of blocks acquired by partitioning a picture intorectangles having an arbitrary size and an arbitrary shape, reducing thecoding amount by using an intra prediction for making a prediction basedon the pixel value of a neighboring block that is in a state in whichcoding and decoding have been completed in a coding process and decodinghas been completed in a decoding process (hereinafter, the state isassumed in which decoding has been completed) and an inter predictionmade through motion compensation based on a picture that has beendecoded.

First, technologies and technical terms used in this example will bedefined.

Chroma Format

In description of the embodiment, the chroma formats of a picture thatis a target for coding and decoding are assumed to be monochrome, 4:2:0,4:2:2, and 4:4:4 that are set as targets also in the AVC/H.264 mode, andcoding and decoding are performed with a luma signal and a chroma signalbeing set as a set. However, the description of the chroma signal willnot be presented for the case of the monochrome. In addition, in amethod for independently coding luma signals and chroma signals in thechroma format of 4:4:4, in this example, the chroma format is assumed tobe the monochrome.

Tree Block and Coding Block

According to the embodiment, as illustrated in FIG. 6, the inside of ascreen is uniformly partitioned in units of squares having a samearbitrary size. This unit is defined as a tree block and is set as abasic unit for address management that is performed for specifying acoding/decoding target block (a coding target block in the codingprocess and a decoding target block in the decoding process) within thepicture. The tree block is configured by one luma signal and two chromasignals except for the case of the monochrome. The size of the treeblock can be freely set to be a size of the power of “2” in accordancewith the picture size or the texture within the screen. The tree blockcan optimize the coding process in accordance with the texture withinthe screen and, as is necessary, can form blocks having a small size byhierarchically partitioning luma signals and chroma signals within thetree block into four parts (forming each two partitions vertically andhorizontally). These blocks are defined as coding blocks and are used asbasic units at the time of performing coding and decoding. The codingblock is configured by one luma signal and two chroma signals except forthe case of the monochrome. A maximum size of the coding block is thesame as the size of the tree block. A coding block of a minimum size ofthe coding block will be referred to as a minimal coding block and canbe freely set to have a size of the power of “2”.

As illustrated in FIG. 6, a coding block A is formed as one coding blockwithout partitioning the tree block. A coding block B is a coding blockacquired by partitioning the tree block into four parts. A coding blockCis a coding block that is acquired by partitioning the tree block intofour parts and partitioning one of the four parts into four parts. Acoding block D is a coding block that is acquired by partitioning thetree block into four parts and hierarchically partitioning one of thefour parts into four parts twice and is a coding block of a minimalsize.

In description made here, it is assumed that the chroma format is 4:2:0,the size of the tree block is set to be 64.times.64 pixels in a lumasignal and 32.times.32 pixels in a chroma signal, and the size of theminimal coding block is set to be 8.times.8 pixels in the luma signaland 4.times.4 pixels in the chroma signal. In the case illustrated inFIG. 6, the size of the coding block A is 64.times.64 pixels in the lumasignal and 32.times.32 pixels in the chroma signal, the size of thecoding block B is 32.times.32 pixels in the luma signal and 16.times.16pixels in the chroma signal, the size of the coding block C is16.times.16 pixels in the luma signal and 8.times.8 pixels in the chromasignal, and the size of the coding block D is 8.times.8 pixels in theluma signal and 4.times.4 pixels in the chroma signal. In addition, in acase where the chroma format is 4:4:4, the sizes of the luma signal andthe chroma signal of each coding block are the same. In a case where thechroma format is 4:2:2, the size of the coding block A is 32.times.64pixels in the chroma signal, the size of the coding block B is16.times.32 pixels in the chroma signal, the size of the coding block Cis 8.times.16 pixels in the chroma signal, and the size of the codingblock D, which is the minimal coding block, is 4.times.8 pixels in thechroma signal.

Prediction Mode

In units of coding blocks, switching between an intra prediction formaking a prediction based on neighboring coded/decoded picture signalsand an inter prediction for making a prediction based on picture signalsof a coded/decoded picture is performed. A mode for identifying theintra prediction or the inter prediction is defined as a prediction modePredMode. The prediction mode PredMode has a value of the intraprediction MODE_INTRA or the inter prediction (MODE_INTER) and is usedfor selective coding.

Partition Mode and Prediction Block

In a case where the intra prediction and the inter prediction are madewith the inside of a screen being partitioned into blocks, in order tofurther decrease the units in which switching between the intraprediction and the inter prediction is performed, the prediction is madewith the coding block being partitioned as is necessary. A mode used foridentifying the method of partitioning luma signals and chroma signalsof the coding block is defined as a partition mode PartMode. Inaddition, the partitioned block is defined as a prediction block. Asillustrated in FIGS. 7A to 7D, four types of partition modes PartModeare defined in accordance with the methods of partitioning luma signalsof the coding block. A partition mode PartMode in which a coding blockis regarded as one prediction block without partitioning luma signals ofthe coding block (FIG. 7A) is defined as 2N.times.2N partitionPART_2N.times.2N, a partition mode PartMode in which a coding block isregarded as two prediction blocks by partitioning luma signals of thecoding block into two parts in the horizontal direction (FIG. 7B) isdefined as 2N.times.N partition PART_2N.times.N, a partition modePartMode in which a coding block is regarded as two prediction blocks bypartitioning luma signals of the coding block into two parts in thevertical direction (FIG. 7C) is defined as N.times.2N partitionPART_N.times.2N, and a partition mode PartMode in which a coding blockis regarded as four prediction blocks by partitioning luma signals ofthe coding block into four parts through horizontal and vertical equalpartitioning (FIG. 7D) is defined as N.times.N partition PART_N.times.N.In addition, chroma signals are also partitioned with the same verticaland horizontal partition ratios of luma signals for each partition modePartMode except for the case of the N.times.N partition PART_N.times.Nof the intra prediction MODE_INTRA. The vertical and horizontalpartition ratios of chroma signals of the coding block of the N.times.Npartition PART_N.times.N of the intra prediction MODE_INTRA differ inaccordance with the type of the chroma format, which will be describedlater.

Inside the coding block, in order to specify each prediction block,numbers starting from “0” are assigned to prediction blocks presentinside the coding block in order of coding. These numbers are defined aspartition indexes PartIdx. A number written inside each prediction blockof a coding block illustrated in FIGS. 7A to 7D represents the partitionindex PartIdx of the prediction block. In the 2N.times.N partitionPART_2N.times.N illustrated in FIG. 7B, the partition index PartIdx ofthe upper prediction block is set as “0”, and the partition indexPartIdx of the lower prediction block is set as “1”. In the N.times.2Npartition PART_N.times.2N illustrated in FIG. 7C, the partition indexPartIdx of the left prediction block is set as “0”, and the partitionindex PartIdx of the right prediction block is set as “1”. In theN.times.N partition PART_N.times.N illustrated in FIG. 7D, the partitionindex PartIdx of the upper left prediction block is set as “0”, thepartition index PartIdx of the upper right prediction block is set as“1”, the partition index PartIdx of the lower left prediction block isset as “2”, and the partition index PartIdx of the lower rightprediction block is set as “3”.

In a case where the prediction mode PredMode is the intra predictionMODE_INTRA, for a coding block other than the coding block D (in thisexample, 8.times.8 pixels in the luma signal) that is the minimal codingblock, the 2N.times.2N partition PART_2N.times.2N is defined as thepartition mode PartMode. On the other hand, only for the coding block Dthat is the minimal coding block, the 2N.times.2N partitionPART_2N.times.2N and the N.times.N partition PART_N.times.N are definedas the partition modes PartMode.

In a case where the prediction mode PredMode is the inter predictionMODE_INTER, for a coding block other than the coding block D that is theminimal coding block, the 2N.times.2N partition PART_2N.times.2N, the2N.times.N partition PART_2N.times.N, and the N.times.2N partitionPART_N.times.2N are defined as the partition modes PartMode. On theother hand, only for the coding block D that is the minimal codingblock, the N.times.N partition PART_N.times.N is defined as thepartition mode PartMode in addition to the 2N.times.2N partitionPART_2N.times.2N, the 2N.times.N partition PART_2N.times.N, and theN.times.2N partition PART_N.times.2N. The reason for not defining theN.times.N partition PART_N.times.N in a coding block other than theminimal coding block is that, for a coding block other than the minimalcoding block, a small coding block can be represented by partitioningthe coding block into four parts.

Intra Prediction and Intra Prediction Mode

In an intra prediction, the values of pixels of the processing targetblock are predicted based on values of pixels of a neighboring decodedblock within the same screen. In a coding device and a decoding deviceof this example, one of intra prediction modes of 34 kinds is selected,and the intra prediction is made. FIG. 8 is a diagram that illustratesvalues of the intra prediction modes and prediction directions definedin this example. The direction indicated by a solid-line arrowrepresents a prediction direction of the intra prediction, in otherwords, a direction that is referred to in the intra prediction, and theintra prediction of a pixel located at a start point of the arrow ismade by referring to a decoded pixel in the direction indicated by thearrow in a neighboring block. Each number represents a value of theintra prediction mode. As the intra prediction modes intraPredMode, inaddition to a vertical prediction (intra prediction modeintraPredMode=0) that makes a prediction in the vertical direction fromthe decoded block located on the upper side, a horizontal prediction(intra prediction mode intraPredMode=1) that makes a prediction in thehorizontal direction from the decoded block located on the left side, anaverage prediction (intra prediction mode intraPredMode=2) that makes aprediction by calculating an average value from a neighboring decodedblock, and an average prediction (intra prediction mode intraPredMode=3)that makes a prediction at the angle of the inclination of 45 degreesfrom a neighboring decoded block, angle predictions (intra predictionmodes intraPredMode=4 to 33) that make predictions of 30 kinds formaking predictions in directions inclined at various angles from aneighboring decoded block are defined.

The intra prediction mode is prepared respectively for luma signals andchroma signals, the intra prediction mode for luma signals is defined asa luma intra prediction mode, and the intra prediction mode for chromasignals is defined as a chroma intra prediction mode. In the coding anddecoding of the luma intra prediction mode, a structure is used in whichthe correlation with the luma intra prediction mode of a neighboringblock is used, in a case where it is determined that a prediction can bemade based on the luma intra prediction mode of a neighboring block onthe coding side, information used for specifying the block that isreferred to is transmitted, and, in a case where it is determined thatanother value may be preferably set to the luma intra prediction moderather than making a prediction based on the luma intra prediction modeof a neighboring block, the value of the luma intra prediction mode isfurther coded or decoded. By predicting the luma intra prediction modeof the coding/decoding target block based on the luma intra predictionmode of the neighboring block, the amount of codes to be transmitted canbe reduced. On the other hand, in the coding and decoding of the chromaintra prediction mode, a structure is used in which the correlation withthe luma intra prediction mode of a prediction block of luma signalsthat is located at the same position as the position of a predictionblock of chroma signals is used, in a case where it is determined that aprediction can be made based on the luma intra prediction mode on thecoding side, a value of the chroma intra prediction mode is predictedbased on the value of the luma intra prediction mode, and, in a casewhere it is determined that an independent value may be preferably setto the chroma intra prediction mode rather than making a predictionbased on the luma intra prediction mode, the value of the chroma intraprediction mode is coded or decoded. By predicting the chroma intraprediction mode based on the luma intra prediction mode, the amount ofcodes to be transmitted can be reduced.

Transform Block

Similarly to a conventional case, also in this embodiment, by using anorthogonal transform for transforming a discrete signal into a frequencydomain such as a discrete cosine transform (DCT) or a discrete sinetransform (DST) and an inverse transform thereof, the amount of codes isreduced. The transform or the inverse transform is performed in units oftransform blocks acquired by hierarchically partitioning a coding blockinto four parts. In the embodiment, four kinds of conversion sizes of32.times.32 pixels, 16.times.16 pixels, 8.times.8 pixels, and 4.times.4pixels are defined, and a 32.times.32 transform, a 16.times.16transform, an 8.times.8 transform, and a 4.times.4 transform and inversetransforms thereof are performed.

Positions of Tree Block, Coding Block, Prediction Block, and TransformBlock

As the position of each block such as the tree block, the coding block,the prediction block, or the transform block described in this example,the position of a pixel of a luma signal that is located at an uppermostand leftmost position on the screen of luma signals is set as the origin(0, 0), and the position of a pixel of a luma signal that is located atthe uppermost and leftmost position included in the area of each blockis represented as two-dimensional coordinates (x, y). The directions ofthe coordinate axes, the rightward side in the horizontal direction andthe downward side in the vertical direction are set as positivedirections, and the unit is one pixel unit of a luma signal. Not only ina case where the chroma format is 4:4:4 in which the picture sizes (thenumbers of pixels) are the same in the luma signal and the chroma signalbut also in a case where the chroma format is 4:2:0 or 4:2:2 in whichthe picture sizes (the numbers of pixels) in the luma signal and thechroma signal are different from each other, the position of each blockof chroma signals is represented by using the coordinates of a pixel ofluma signals included in the area of the block, and the unit is onepixel of a luma signal. In this way, it is apparent that the position ofeach block of chroma signals can be specified, and, by only comparingthe values of coordinates, the relation between the positions of theblock of luma signals and the block of chroma signals becomes clear.FIG. 9 is a diagram that illustrates an example of the positions ofblocks defined in this example in a case where the chroma format is4:2:0. In FIG. 9, “x” represents the position of a pixel of a lumasignal on the plane of a screen, and “.largecircle.” represents theposition of a pixel of a chroma signal. A dotted-line rectangleillustrated in FIG. 9 is a block E of luma signals of 8.times.8 pixelsand is also a block F of chroma signals of 4.times.4 pixels. Inaddition, “.tangle-solidup.” is the position of a pixel of a lumasignal, which is located at an uppermost and leftmost position, in theblock E of the luma signals of the 8.times.8 pixels represented bydotted lines. Accordingly, “.tangle-solidup.” is the position of theblock E of the luma signals of the 8.times.8 pixels represented bydotted lines, and the coordinates of a luma signal of a pixelrepresented by “.tangle-solidup.” are the coordinates of the block E ofluma signals of the 8.times.8 pixels represented by the dotted lines.Similarly, “.tangle-solidup.” is the position of a pixel of a lumasignal, which is located at an uppermost and leftmost position, includedin the area of the block F of chroma signals of the 4.times.4 pixelsrepresented by the dotted lines as well. Accordingly, “.tangle-solidup.”is the position of the block F of chroma signals of 4.times.4 pixelsrepresented by the dotted lines, and the coordinates of a luma signal ofa pixel represented by “.tangle-solidup.” are the coordinates of theblock F of chroma signals of the 4.times.4 pixels represented by thedotted lines. In the embodiment, regardless of the type of the chromaformat and the shape and the size of the block, only in a case where thex component and the y component of the coordinates of the block of lumasignals, which is defined, and the coordinates of the block of chromasignals are all the same, such blocks are defined to be located at thesame position.

FIG. 1 is a block diagram that illustrates the configuration of apicture coding device according to the embodiment. The picture codingdevice according to the embodiment is equipped with a chroma formatsetting unit 101, a picture memory 102, an intra prediction unit 103, aninter prediction unit 104, a coding method decision unit 105, a residualsignal generation unit 106, an orthogonal transform/quantization unit107, an inverse quantization/inverse orthogonal transform unit 108, adecoding picture signal superimposition unit 109, a decoded picturememory 111, a first bitstream constructing unit 112, a second bitstreamconstructing unit 113, a third bitstream constructing unit 114, and abitstream multiplexing unit 115.

The chroma format setting unit 101 sets the chroma format of a picturesignal that is a coding target. It may be configured such that a chromaformat is determined based on a coding picture signal supplied to thechroma format setting unit 101, and the chroma format is set, or achroma format may be externally set. The information of the chromaformat in which only the luma signal is set to 4:2:0, 4:2:2, or 4:4:4 issupplied to the first bitstream constructing unit 112 and also to thesecond bitstream constructing unit 113, and a coding process that isbased on the chroma format is performed. In addition, although notillustrated in the figure, also in the picture memory 102, the intraprediction unit 103, the inter prediction unit 104, the coding methoddecision unit 105, the residual signal generation unit 106, theorthogonal transform/quantization unit 107, the inversequantization/inverse orthogonal transform unit 108, the decoding picturesignal superimposition unit 109, and the third bitstream constructingunit 114 illustrated in FIG. 1, a coding process is performed based onthe set chroma format, and information is managed in the codinginformation storing memory 110 and the decoded picture memory 111 basedon the set chroma format.

In the picture memory 102, picture signals that are coding targetssupplied in order of time are temporarily stored. The picture signalsthat are coding targets stored in the picture memory 102 are sorted, arepartitioned in units of coding blocks in a plurality of combinationsaccording to the setting, are further partitioned in units of predictionblocks, and are supplied to the intra prediction unit 103 and the interprediction unit 104.

The intra prediction unit 103, in units of prediction blocks accordingto each partition mode PartMode in units of a plurality of codingblocks, makes intra predictions corresponding to a plurality of lumaintra prediction modes and chroma intra prediction modes for lumasignals and chroma signals of the prediction block that is a codingtarget based on the decoded picture signals stored in the decodedpicture memory 111, thereby acquiring intra prediction signals. Inaddition, as the chroma intra prediction mode, a value predicted basedon the luma intra prediction mode in accordance with the chroma formator one of “0” (horizontal direction), “1” (vertical direction), “2”(average), and “3” (inclination of 45 degrees), which are representativeintra prediction modes, is selected to be limited thereto. Here, amethod of predicting the chroma intra prediction mode based on the lumaintra prediction mode will be described later.

By subtracting an intra prediction signal in units of prediction blocksfrom the signal that is the coding target supplied in units ofprediction blocks for each pixel, a predicted residual signal isacquired. An evaluation value used for evaluating the code amount andthe distortion amount is calculated by using the predicted residualsignal, a mode that is optimal from the viewpoint of the code amount andthe distortion amount is selected in units of prediction blocks fromamong a plurality of intra prediction modes, and intra predictioninformation, an intra prediction signal, and an evaluation value of theintra prediction corresponding to the intra prediction mode selected asa candidate for the intra prediction of the prediction block aresupplied to the coding method decision unit 105. The predictionprocessing units in which the intra prediction is made will be describedlater.

The inter prediction unit 104 performs inter predictions according to aplurality of inter prediction modes (an L0 prediction, an L1 prediction,and both predictions) and a reference picture based on decoded picturesignals stored in the decoded picture memory 111 in units correspondingto the partition modes PartMode of a plurality of coding block units, inother words, in units of prediction blocks, thereby acquiring interprediction signals. At that time, a motion vector search is performed,and the inter prediction is made in accordance with the searched motionvector. In addition, in the case of the both predictions, by averagingtwo inter prediction signals for each pixel or performing weightedaddition thereof, the inter predictions of both the predictions areperformed. An inter prediction signal in units of prediction blocks issubtracted from the signal of the coding target supplied in units ofprediction blocks for each pixel, thereby deriving a predicted residualsignal. An evaluation value used for evaluating the code amount and thedistortion amount is calculated by using the predicted residual signal,a mode that is optimal from the viewpoint of the code amount and thedistortion amount is selected from among the plurality of interprediction modes in units of prediction blocks, and the inter predictioninformation, the inter prediction signal, and the evaluation value ofthe inter prediction corresponding to the selected inter prediction modeas a candidate for the inter prediction of the prediction block aresupplied to the coding method decision unit 105.

The coding method decision unit 105 determines a partition method, aprediction mode PredMode, and a partition mode PartMode of the codingblock, which is optimal, based on the intra prediction evaluation valuecorresponding to the intra prediction information and the interprediction evaluation value corresponding to the inter predictioninformation that are selected in each prediction block in units of aplurality of coding blocks, supplies coding information that includesthe intra prediction information or the inter prediction informationaccording to the determination to the second bitstream constructing unit113, stores the coding information in the coding information storingmemory 110, and supplies a prediction signal that has beenintra-predicted or inter-predicted according to the determination to theresidual signal generation unit 106 and the decoding picture signalsuperimposition unit 109.

The residual signal generation unit 106 generates a residual signal bysubtracting the prediction signal that has been intra-predicted orinter-predicted from the picture signal to be coded for each pixel andsupplies the residual signal to the orthogonal transform/quantizationunit 107.

The orthogonal transform/quantization unit 107 generates an orthogonallytransformed and quantized residual signal by performing an orthogonaltransform and quantization for transforming the residual signal to besupplied into a frequency domain such as a DCT or a DST in accordancewith a quantization parameter and supplies the orthogonally transformedand quantized residual signal to the third bitstream constructing unit114 and the inverse quantization/inverse orthogonal transform unit 108.

The first bitstream constructing unit 112 calculates values of syntaxelements relating to coding information in units of sequences, pictures,and slices in accordance with a semantics rule used for defining themeaning and the deriving method of the syntax elements, constructs afirst bitstream by performing entropy coding of the calculated value ofeach syntax element through variable-length coding, arithmetic coding,or the like in accordance with the syntax rule, and supplies the codedfirst bitstream to the bitstream multiplexing unit 115. In addition, thevalue of the syntax element relating to the chroma format is calculatedby the first bitstream constructing unit 112. The syntax elementrelating to the chroma formation is calculated based on the chromaformat information that is supplied from the chroma format setting unit101. FIG. 10 is an example of the definition of syntax at the time ofcoding the chroma format information using the sequence parameter setthat is a header used for coding information relating to coding of theentire sequence defined in this example. A syntax elementchroma_format_idc represents the type of the chroma format. As themeaning of the syntax chroma_format_idc, a value 0 representsmonochrome, a value 1 represents 4:2:0, a value 2 represents 4:2:2, anda value 3 represents 4:4:4. In addition, the meaning of the syntaxelement separate_colour_plane_flag represents whether or not a lumasignal and chroma signals are separately coded. A case where the valueof the syntax element separate_colour_plane_flag is “0” represents thattwo chroma signals are coded with being associated with the luma signal.A case where the value of the syntax element chroma_format_idc is “1”represents that the luma signal and the two chroma signals areseparately coded. Only in a case where the value of the syntax elementchroma_format_idc is “3”, in other words, in a case where the chromaformat is 4:4:4, the value of the syntax element chroma_format_idc canbe set to “0” or “1”, and, for any other chroma format, the value of thesyntax element separate_colour_plane_flag is constantly coded with being“0”.

The second bitstream constructing unit 113 calculates the value of thesyntax element relating to the coding information determined by thecoding method decision unit 105 for each prediction block in addition tothe coding information in units of coding blocks in accordance with thesemantics rule that defines the meaning and the deriving method of thesyntax element. More particularly, in addition to the coding informationin units of coding blocks such as the partition method, the predictionmode PredMode, and the partition mode PartMode of the coding block, thevalue of the syntax element relating to the coding information in unitsof prediction blocks is calculated. In a case where the prediction modePredMode is the intra prediction, the values of the syntax elementsrelating to the intra prediction mode including the luma intraprediction mode and the chroma intra prediction mode are calculated. Onthe other hand, in a case where the prediction mode PredMode is theinter prediction, the values of syntax elements relating to the interprediction mode, information used for specifying a reference picture,and the inter prediction information such as a motion vector arecalculated. Entropy coding using variable-length coding, arithmeticcoding, or the like is performed for the calculated value of each syntaxelement in accordance with the syntax rule, a second bitstream isconstructed, and the coded second bitstream is supplied to the bitstreammultiplexing unit 115. Detailed processing contents relating to thecalculation of syntax elements and the entropy coding relating to theluma intra prediction mode and the chroma intra prediction mode that areperformed by the second bitstream constructing unit 113 will bedescribed later.

The third bitstream constructing unit 114 constructs a third bitstreamby performing entropy coding of the orthogonally-transformed andquantized residual signal through the variable-length coding, arithmeticcoding, or the like in accordance with the defined syntax rule andsupplies the third bitstream to the bitstream multiplexing unit 115.

The bitstream multiplexing unit 115 constructs a bitstream bymultiplexing the first bitstream, the second bitstream, and the thirdbitstream in accordance with a defined syntax rule and outputs themultiplexed bitstream.

The inverse quantization/inverse orthogonal transform unit 108calculates a residual signal by performing inverse quantization andinverse orthogonal transform of the orthogonally-transformed andquantized residual signal that is supplied from the orthogonaltransform/quantization unit 107 and supplies the calculated residualsignal to the decoding picture signal superimposition unit 109. Thedecoding picture signal superimposition unit 109 constructs a decodedpicture by superimposing the prediction signal that has beenintra-predicted or inter-predicted in accordance with the determinationmade by the coding method decision unit 105 and the residual signal thathas been inversely-quantized and inversely-orthogonal transformed by theinverse quantization/inverse orthogonal transform unit 108 each otherand stores the constructed decoded picture in the decoded picture memory111. In addition, a filtering process for decreasing block distortion orthe like due to coding may be performed for the decoded picture, and theprocessed decoded picture may be stored in the decoded picture memory111.

FIG. 2 represents blocks that illustrate the configuration of a picturedecoding device, which corresponds to the picture coding deviceillustrated in FIG. 1, according to an embodiment. The picture decodingdevice according to the embodiment is equipped with a bitstreamsplitting unit 201, a first bitstream decoding unit 202, a secondbitstream decoding unit 203, a third bitstream decoding unit 204, achroma format managing unit 205, an intra prediction unit 206, an interprediction unit 207, an inverse quantization/inverse orthogonaltransform unit 208, a decoding picture signal superimposition unit 209,a coding information storing memory 210, a decoded picture memory 211,and switches 212 and 213.

A bitstream supplied to the bitstream splitting unit 201 is split inaccordance with a defined syntax rule, a first bitstream representingcoding information in units of sequences, pictures, and slices issupplied to the first bitstream decoding unit 202, a second bitstreamincluding coding information in units of coding blocks is supplied tothe second bitstream decoding unit 203, and a third bitstream includingan orthogonally transformed and quantized residual signal is supplied tothe third bitstream decoding unit 204.

The first bitstream decoding unit 202 performs entropy decoding of thesupplied first bitstream in accordance with a syntax rule and acquiresvalues of syntax elements relating to the coding information in units ofsequences, pictures, and slices. The coding information in units ofsequences, pictures, and slices is calculated based on values of syntaxelements relating to the coding information, which has been decoded, inunits of sequences, pictures, and slices in accordance with a semanticsrule used for defining the meaning and the deriving method of the syntaxelements. The first bitstream decoding unit 202 is a bitstream decodingunit that corresponds to the first bitstream constructing unit 112disposed on the coding side and has a function for returning thebitstream including the coding information in units of sequences,pictures, and slices, which has been coded by the first bitstreamconstructing unit 112 to each coding information. The chroma formatinformation coded by the first bitstream constructing unit 112 iscalculated based on the value of the syntax element relating to chromaformat information that is acquired by performing entropy decoding ofthe second bitstream using the first bitstream decoding unit 202. Inaccordance with the syntax rule illustrated in FIG. 10 and the semanticsrule, the type of the chroma format is specified based on the value ofthe syntax element chroma_format_idc, and, as the value of the syntaxelement chroma_format_idc, “0” represents monochrome, “1” represents4:2:0, “2” represents 4:2:2, and “3” represents 4:4:4. In addition, in acase where the value of the syntax element chroma_format_idc is “3”, thesyntax element separate_colour_plane_flag is decoded, and it isdetermined whether or not a luma signal and chroma signals areseparately coded. The calculated chroma format information is suppliedto the chroma format managing unit 205.

The chroma format managing unit 205 manages the supplied chroma formatinformation. The supplied chroma format information is supplied to thesecond bitstream decoding unit 203, and the process of calculatingcoding information of a coding block and a prediction block based on thechroma format information is performed. Although not illustrated in thefigure, also in the third bitstream decoding unit 204 and the intraprediction unit 206, the inter prediction unit 207, the inversequantization/inverse orthogonal transform unit 208, and the decodingpicture signal superimposition unit 209 illustrated in FIG. 2, adecoding process based on the chroma format information is performed,and data is managed based on the chroma format information in the codinginformation storing memory 210 and the decoded picture memory 211.

The second bitstream decoding unit 203 performs entropy decoding of thesupplied first bitstream in accordance with the syntax rule, therebyacquiring values of syntax elements relating to the coding informationin units of coding blocks and prediction blocks. In accordance with thesemantics rule that defines the meaning and deriving method of thesyntax elements, the coding information in units of coding blocks and inunits of prediction blocks is calculated based on the values of thesyntax elements relating to the supplied coding information in units ofcoding blocks and in units of prediction blocks. The second bitstreamdecoding unit 203 is a coding information calculating unit thatcorresponds to the second bitstream constructing unit 113 disposed onthe coding side and has a function for returning the second bitstreamincluding the coding information in units of coding blocks and in unitsof prediction blocks, which has been coded by the second bitstreamconstructing unit 113, to each coding information. More specifically,based on each syntax element acquired by decoding the second bitstreamin accordance with the defined syntax rule, in addition to the partitionmethod, the prediction mode PredMode, and the partition mode PartMode ofthe coding block, in a case where the prediction mode PredMode is theintra prediction, an intra prediction mode that includes the luma intraprediction mode and the chroma intra prediction mode is acquired. On theother hand, in a case where the prediction mode PredMode is the interprediction, inter prediction information such as the inter predictionmode, information used for specifying a reference picture, and a motionvector is acquired. In a case where the prediction mode PredMode is anintra prediction, the intra prediction mode including the luma intraprediction mode and the chroma intra prediction mode is supplied to theintra prediction unit 206 through the switch 212. In a case where theprediction mode PredMode is the inter prediction, the inter predictioninformation such as the inter prediction mode, information used forspecifying a reference picture, and a motion vector is supplied to theinter prediction unit 207 through the switch 212. Detailed processesrelating to the entropy decoding process performed by the secondbitstream decoding unit 203 and the process of calculating the values ofthe luma intra prediction mode and the chroma intra prediction modebased on the syntax elements relating to the luma intra prediction modeand the chroma intra prediction mode will be described later.

The third bitstream decoding unit 204 calculates an orthogonallytransformed and quantized residual signal by decoding the suppliedbitstream and supplies the orthogonally transformed and quantizedresidual signal to the inverse quantization/inverse orthogonal transformunit 208.

The intra prediction unit 206 generates a predicted picture signal byperforming an intra prediction based on a decoded neighboring blockstored in the decoded picture memory 211 in accordance with the suppliedintra prediction mode including the luma intra prediction mode and thechroma intra prediction mode and supplies the predicted picture signalto the decoding picture signal superimposition unit 209 through theswitch 213. In addition, the units in which the intra prediction is madewill be described later. In this embodiment, when the value of thechroma intra prediction mode is predicted based on the value of the lumaintra prediction mode, the method of deriving the chroma intraprediction mode differs in accordance with the chroma format. In such acase, intra prediction is made using the intra prediction mode derivedusing the method that differs in accordance with the chroma format. Themethod of deriving the chroma intra prediction mode to be describedlater will be described later.

The inter prediction unit 207 generates a predicted picture signal bymaking an inter prediction using motion compensation based on thedecoded reference picture stored in the decoded picture memory 211 byusing the inter prediction mode, the information used for specifying thereference picture, and the inter prediction information such as a motionvector, which are to be supplied, and supplies the predicted picturesignal to the decoding picture signal superimposition unit 209 throughthe switch 213. In addition, in the case of the both predictions, afinal predicted picture signal is generated by adaptably multiplying twomotion compensation predicted picture signals of the L0 and L1predictions by weighing factors and superimposing the predicted picturesignals each other.

The inverse quantization/inverse orthogonal transform unit 208 performsan inverse orthogonal transform and inverse quantization of theorthogonally transformed and quantized residual signal that has beendecoded by the third bitstream decoding unit 204, thereby acquiring aninversely-orthogonal transformed and inversely-quantized residualsignal.

The decoding picture signal superimposition unit 209 decodes thedecoding picture signal by superimposing the predicted picture signalthat has been predicted by the intra prediction unit 206 or the interprediction unit 207 and the residual signal that has beeninversely-orthogonal transformed and inversely quantized by the inversequantization/inverse orthogonal transform unit 208 each other and storesthe decoding picture signal in the decoded picture memory 211. When thedecoded picture is stored in the decoded picture memory 211, a filteringprocess for decreasing block distortion or the like due to coding may beperformed for the decoded picture before the decoded picture is storedin the decoded picture memory 211. The decoding picture signals storedin the decoded picture memory 211 are output in the output order.

Next, the prediction processing units in which the intra prediction ismade, which is one of the features of the embodiment, will be describedin detail.

First, a minimal unit of the orthogonal transform according to thisexample will be described. By using a characteristic of picture codingin which, while degradation in the picture quality of a low frequencycomponent easily stands out, degradation in the picture quality of ahigh frequency component does not easily stand out, the code amount isreduced by quantizing the high frequency component more roughly than thelow frequency component. However, in the case of the 2.times.2conversion, it is difficult to sufficiently divide the signal intosufficient number of frequency components, and accordingly, thereduction effectiveness of the code amount is low. In addition, in acase where the processing unit of the intra prediction, thetransformation, and the quantization is too small, the number ofprocessing units corresponding thereof increases, whereby the processingbecomes complex. Thus, in this example, the minimal unit of theorthogonal transform is set as 4.times.4 pixels.

Next, a minimal unit of the intra prediction made in this example, inother words, a minimal size of the prediction block in the case of theintra prediction will be described. In the intra prediction, since thepixel value of the processing target block is predicted based on thepixel values of a neighboring block that has been decoded within thesame screen, it is necessary to complete the decoding process before thecoding and decoding process of the subsequent block. More specifically,by using the prediction signal acquired by the intra prediction, aresidual signal is calculated, an orthogonal transform, quantization,inverse-quantization, and inverse transform are performed for theresidual signal, and a resultant signal is superimposed with theprediction signal, whereby the decoding process is completed, and astate is formed in which an intra prediction of a subsequent block canbe made. Accordingly, it is necessary to perform the intra prediction inunits of which the size is equal to or larger than the size of theminimal transform block. The reason for this is that, when the intraprediction is made in units of which the size is smaller than the sizeof the minimal transform block, thereafter, an orthogonal transformcannot be performed, and the decoding process cannot be performed.Accordingly, in this example, a minimal unit of the intra prediction, inother words, a minimal size of the prediction block at the time ofperforming the intra prediction is set as 4.times.4 pixels that is thesame as the minimal unit of the orthogonal transform.

Next, a minimal size of the coding block according to this example willbe described. In the minimal coding block, the partition mode PartModeis defined to be the N.times.N partition in both the intra predictionMODE_INTRA and the inter prediction of the prediction mode PredMode.While the N.times.N partition is a partition mode PartMode in which acoding block is partitioned into four prediction blocks throughhorizontal and vertical equal partition of luma signals of the codingblock, the minimal unit of the intra prediction according to thisexample is set as 4.times.4 pixels, and accordingly, the minimal size ofthe coding block is 8.times.8 pixels in the luma signal.

Next, the method of partitioning chroma signals of the coding block forthe N.times.N partition at the time of performing an intra predictionwill be described. FIGS. 11A to 11D are diagrams that illustrate methodsof partitioning chroma signals of a coding block for the N.times.Npartition at the time of performing the intra prediction.

In a case where the chroma format is 4:2:0, when the minimal size of thecoding block is 8.times.8 pixels in the luma signal, the minimal size ofthe coding block is 4.times.4 pixels in the chroma signal, and thecoding block cannot be further partitioned. Thus, in this embodiment, ina case where the chroma format is 4:2:0, when the prediction mode is theintra prediction, and the partition mode PartMode is the N.times.Npartition, as illustrated in FIG. 11A, an intra prediction is made inunits of 4.times.4 pixels with the coding block being partitioned intofour prediction blocks through horizontal and vertical equal partitionof the coding block in the luma signal. However, in the chroma signal,as illustrated in FIG. 11B, the coding block is not partitioned and isset as one prediction block, and an intra prediction is made in units of4.times.4 pixels of which the size is the same as the size of theprediction block of luma signals. In addition, the partition indexPartIdx of the prediction block of chroma signals is set to “0”.

In a case where the chroma format is 4:2:2, when the minimal size of thecoding block is 8.times.8 pixels in the luma signal, the minimal size ofthe coding block is 4.times.8 pixels in the chroma signal, and thecoding block can be equally partitioned horizontally but cannot beequally partitioned vertically. Thus, in this embodiment, in a casewhere the chroma format is 4:2:2, when the prediction mode is the intraprediction, and the partition mode PartMode is the N.times.N partition,as illustrated in FIG. 11A, in the luma signal, an intra prediction ismade in units of 4.times.4 pixels with the coding block beingpartitioned into four prediction blocks through horizontal and verticalequal partition of the coding block. However, in the chroma signal, asillustrated in FIG. 11C, the coding block is equally partitioned onlyhorizontally without being vertically partitioned, and an intraprediction is made in units of 4.times.4 pixels with the coding blockbeing set as two prediction blocks. In addition, the partition indexesPartIdx of the prediction blocks of chroma signals are set to “0” and“2” in the coding order (order from the upper side to the lower side).The reason for setting the partition index PartIdx of the lower block to“2” is that the lower prediction block of chroma signals is located atthe same position as the position of the prediction block of which thepartition index PartIdx of the luma signals is “2”.

The prediction block of chroma signals and the prediction block of lumasignals being at the same position represents that, when the coordinatesof the uppermost and leftmost pixel of each prediction block is set asthe reference position, the reference positions of the prediction blockof chroma signals and the prediction block of luma signals being thesame.

In a case where the chroma format is 4:4:4, when the minimal size of thecoding block is 8.times.8 pixels in the luma signal, the minimal size ofthe coding block is 8.times.8 pixels in the chroma signal, and,similarly to the luma signal, the coding block can be partitioned intofour prediction blocks through horizontal and vertical equal partition.Thus, in this embodiment, in a case where the chroma format is 4:4:4,when the prediction mode is the intra prediction, and the partition modePartMode is the N.times.N partition, as illustrated in FIG. 11A, in theluma signal, an intra prediction is made in units of 4.times.4 pixelswith the coding block being partitioned into four prediction blocksthrough horizontal and vertical equal partition of the coding block,and, also in the chroma signal, as illustrated in FIG. 11C, an intraprediction is made in units of 4.times.4 pixels with the coding blockbeing partitioned into four prediction blocks through horizontal andvertical equal partition of the coding block. In addition, similarly tothe luma signal, the partition indexes PartIdx of the prediction blocksof chroma signals are set to “0”, “1”, “2”, and “3” in the coding order(the order of the upper left side, the upper right side, the lower leftside, and the lower right side).

In the embodiment, regardless of the type of the chroma format, in acase where the values of the partition index PartIdx of the predictionblock of the luma signals and the partition index PartIdx of theprediction block of the chroma signals are the same, the coordinates(the coordinates of a pixel located at the uppermost and leftmostposition in the prediction block) representing the position of theprediction block of the luma signals and the coordinates (thecoordinates of a pixel located at the uppermost and leftmost position inthe prediction block) representing the position of the prediction blockof the chroma signals are the same, and accordingly, the predictionblocks are located at the same position.

Next, in a case where the chroma format is 4:2:0, a case will beconsidered in which a coding block is partitioned into four parts inboth the luma signal and the chroma signal through N.times.N partitionof the inter prediction, and, a prediction block is formed such that theluma signal is 4.times.4 pixels, and the chroma signal is 2.times.2pixels. In the inter prediction, in both the luma signal and the chromasignal, the inter prediction is made through motion compensation usingcommon coding information. However, in the motion compensation of achroma signal of which the chroma format is 4:2:0, a value acquired byscaling both the horizontal and vertical components half in themagnitude of the value of the reference motion vector through the lumasignal is used. In the inter prediction, as is different from the intraprediction, the decoding signal of a neighboring block within the samepicture is not used, and accordingly, an inter prediction processingunit that is smaller than the orthogonal transform processing unit canbe used. Accordingly, since the orthogonal transform can be performed inunits larger than the prediction block, even in a case where the codingblock is partitioned into four parts in the chroma signal, and the interprediction is made in units of 2.times.2 pixels, the orthogonaltransform does not need to be performed necessarily in units of2.times.2 pixels, and, by combining four prediction blocks after theinter predictions of the four prediction blocks and calculating aresidual signal in units of 4.times.4 pixels, the orthogonal transformcan be performed in units of 4.times.4 pixels.

Next, in a case where the chroma format is 4:2:2, a case will beconsidered in which a coding block is partitioned into four parts inboth the luma signal and the chroma signal through the N.times.Npartition of the inter prediction, and, a prediction block is formedsuch that the luma signal is 4.times.4 pixels, and the chroma signal is2.times.4 pixels. In the inter prediction, in both the luma signal andthe chroma signal, the inter prediction is made through motioncompensation using common coding information. However, in the motioncompensation of a chroma signal of which the chroma format is 4:2:2, asthe luma signal, for the vertical component, the original value of themagnitude of the reference motion vector is used, and a value acquiredby half scaling of the horizontal component is used. Similarly to thecase where the chroma format is 4:2:0, the orthogonal transform can beperformed in units larger than the prediction block, and accordingly,even in a case where the coding block is partitioned into four parts inthe chroma signal, and the inter prediction is made in units of2.times.4 pixels, the orthogonal transform does not need to be performednecessarily in units of 2.times.2 pixels, and, by combining twoprediction blocks that are aligned in the horizontal direction after theinter predictions of the four prediction blocks and calculating aresidual signal in units of two 4.times.4 pixels, the orthogonaltransform can be performed in units of 4.times.4 pixels.

Therefore, in the N.times.N partition of the inter prediction,regardless of the type of the chroma format, both the luma signals andthe chroma signals are equally partitioned horizontally and verticallyso as to form four prediction blocks.

Next, the coding process of the coding information in units of codingblocks and prediction blocks that is performed by the second bitstreamconstructing unit 113 illustrated in FIG. 1 will be described withfocusing on points relating to the intra prediction mode that is afeature of the embodiment. FIG. 12 is a block diagram that illustratesthe configuration of the second bitstream constructing unit 113illustrated in FIG. 1.

As illustrated in FIG. 12, the second bitstream constructing unit 113illustrated in FIG. 1 is configured by: a syntax element calculatingunit 121 relating to the coding information in units of coding blocks; asyntax element calculating unit 122 relating to the luma intraprediction mode; a syntax element calculating unit 123 relating to thechroma intra prediction mode; a syntax element calculating unit 124relating to the inter prediction information; an intra prediction modecoding control unit 125; and an entropy coding unit 126. In each unitconfiguring the second bitstream constructing unit 113, a processcorresponding to the chroma format information supplied from the chromaformat setting unit 101 is performed, and a process corresponding to thecoding information of the prediction mode, the partition mode PartMode,and the like in units of coding blocks is performed.

The syntax element calculating unit 121 relating to the codinginformation in units of coding blocks calculates the value of the syntaxelement relating to the coding information in units of coding blocks andsupplies the calculated value of the syntax element to the entropycoding unit 126. The values of the syntax elements relating to theprediction mode PredMode used for determining the intra predictionMODE_INTRA or the inter prediction MODE_INTER of the coding block andthe partition mode PartMode used for determining the shape of theprediction block are calculated by the syntax element calculating unit121 relating to the coding information in units of the coding blocks

The syntax element calculating unit 122 relating to the luma intraprediction mode, in a case where the prediction mode PredMode of thecoding block is the intra prediction MODE_INTRA, calculates the valuesof syntax element relating to the luma intra prediction mode of theprediction block of the luma signal and supplies the calculated value ofthe syntax element to the entropy coding unit 126. The syntax elementsrelating to the luma intra prediction mode are a syntax elementprev_intra_lumapred_flag[x0][y0] that is a flag representing whether ornot a prediction can be made based on the luma intra prediction mode ofthe neighboring block, a syntax element mpm_idx[x0][y0] that is an indexindicating a prediction block as a prediction source, and a syntaxelement rem_intra_luma_pred_mode[x0][y0] that represents the luma intraprediction mode in units of prediction blocks. Here, x0 and y0 arecoordinates that represent the position of the prediction block. In thecalculation of the value of the syntax element relating to the lumaintra prediction mode, the correlation with the luma intra predictionmode of a neighboring block stored in the coding information storingmemory 110 is used. In a case where the prediction can be made based onthe luma intra prediction mode of the neighboring block, a syntaxelement prev_intra_luma_pred_flag[x0][y0], which is a flag representingthe use of the value, is set to “1” (true), and a value used forspecifying a reference destination is set to the syntax elementmpm_idx[x0][y0] that is an index indicating a prediction block of theprediction source. On the other hand, in a case where a predictioncannot be made, the syntax element prev_intra_luma_pred_flag[x0][y0] isset to “0” (false), and a value used for specifying the luma intraprediction mode is set to the syntax elementrem_intra_luma_pred_mode[x0][y0] that represents the luma intraprediction mode to be coded.

The number of luma intra prediction modes of the prediction block withinthe coding block differs in accordance with the partitioned block. Thus,in a case where the partition mode PartMode is the 2N.times.2Npartition, the values of the syntax elements relating to the luma intraprediction mode of the prediction blocks of one set are calculated foreach coding block. In a case where the partition mode is the N.times.Npartition, the values of the syntax elements relating to the luma intraprediction modes of prediction blocks of four sets are calculated foreach coding block.

The syntax element calculating unit 123 relating to the chroma intraprediction mode, in a case where the prediction mode PredMode of thecoding block is the intra prediction MODE_INTRA, calculates the value ofthe syntax element intra_chroma_pred_mode[x0][y0] relating to the chromaintra prediction mode of the prediction block of chroma signals andsupplies the calculated value of the syntax elementintra_chroma_pred_mode[x0][y0] to the entropy coding unit 126. In thecalculation of the value of the syntax element relating to the chromaintra prediction mode, the correlation with the luma intra predictionmode of the prediction block of luma signals that is located at the sameposition as the position of the prediction block of chroma signals isused. Thus, in a case where a chroma intra prediction mode can bepredicted based on the luma intra prediction mode of the predictionblock of luma signals that is located at the same position as theposition of the prediction block of chroma signals, the value of thechroma intra prediction mode is predicted based on the value of the lumaintra prediction mode. On the other hand, in a case where the chromaintra prediction mode cannot be predicted based on the luma intraprediction mode, a structure is used in which any one of values “0”(horizontal direction), “1” (horizontal direction), “2” (average value),and “3” (inclination of 45 degrees), which are representative in intraprediction modes, is set to the chroma intra prediction mode. As aresult, the code amount is reduced.

Here, a method of predicting the value of the chroma intra predictionmode based on the value of the luma intra prediction mode and the valueof the syntax element relating to the chroma intra prediction mode onthe decoding side will be described. FIG. 14 is a conversion table usedfor calculating the value of the chroma intra prediction mode based onthe value of the syntax element intra_chroma_pred_mode[x0][y0] relatingto the chroma intra prediction mode defined in this example and thevalue of the luma intra prediction mode of the prediction block locatedat the same position as the position of the prediction block of chromasignals. By using this conversion table, the value of the chroma intraprediction mode is calculated on the decoding side.

In a case where the value of the syntax elementintra_chroma_pred_mode[x0][y0] is “0”, the value of the chroma intraprediction mode is predicted in accordance with the chroma format basedon the value of the luma intra prediction mode of the prediction blocklocated at the same position as the position of the prediction block ofchroma signals.

In a case where the chroma format is 4:2:0 or 4:4:4, and the value ofthe syntax element intra_chroma_pred_mode[x0][y0] is “0”, the value ofthe luma intra prediction mode of the prediction block located at thesame position as the position of the prediction block of chroma signalsis directly set as the value of the chroma intra prediction mode.

In a case where the chroma format is 4:2:2 and the value of the syntaxelement intra_chroma_pred_mode[x0][y0] is “0”, based on a conversiontable illustrated in FIG. 15, the value of the chroma intra predictionmode is calculated in accordance with the value of the luma intraprediction mode of the prediction block located at the same position asthe position of the prediction block of chroma signals. FIG. 15 is aconversion table used for predicting the value of the chroma intraprediction mode based on the value of the luma intra prediction mode ofthe prediction block located at the same position as the position of theprediction block of chroma signals in a case where the chroma format is4:2:2 that is defined in this example.

In a case where the chroma format is 4:2:2, when the value of the chromaintra prediction mode is predicted based on the value of the luma intraprediction mode, the reason for not using the original value, unlike thecase of the chroma format of 4:2:0 or 4:4:4, but calculating the valueusing the conversion table illustrated in FIG. 15 will be described. Thechroma format of 4:2:2, as illustrated in FIG. 3B, is a chroma format inwhich chroma signals are sampled to have a half density of the densityof luma signals in the horizontal direction and to have the same densityas the density of the luma signals in the vertical direction.Accordingly, when an intra prediction of a chroma signal is performed ina prediction direction acquired by performing ½ times scaling in thehorizontal direction for each prediction direction of the luma intraprediction mode or in a prediction direction neighboring thereto, aresult that is the same as or close to that of the intra prediction ofthe luma signal of the prediction block located at the same position asthe position of the prediction block of the chroma signal is acquired.

This will be described in detail with reference to FIGS. 27A and 27B.FIGS. 27A and 27B are diagrams that illustrate the correspondencerelation between the prediction directions of intra predictions of aluma signal and a chroma signal in a case where the chroma format is4:2:2. In FIGS. 27A and 27B, “x” represents the position of a pixel of aluma signal, and “.largecircle.” represents the position of a pixel of achroma signal. In the case where the chroma format is 4:2:2, the chromasignals are sampled in the horizontal direction at a half ratio of thatof luma signals. FIG. 27A represents the positions of sampled pixels ofluma signals and chroma signals of 4:2:2. Reference sign P1 represents apixel that is intra-predicted, and reference sign P2 represents a pixel(actually, a pixel neighboring thereto is also referred to due to afiltering process) that is referrer to at the time of making the intraprediction. An arrow, which is denoted by reference sign 2701, directingfrom the pixel P1 to the pixel P2 represents the intra predictiondirection of the pixel P1 of the luma signal and represents the intraprediction direction of the pixel P1 of the chroma signal.

FIG. 27B represents the array of pixels of chroma signals that have beensampled at a half ratio in the horizontal direction. Here, when an intraprediction of a chroma signal is made, in a case where ½ scaling is notperformed in the horizontal direction, the intra prediction direction ofthe pixel P1 of the chroma signal is the direction of an arrow denotedby reference sign 2702, and in the pixel array of chroma signals, thepixel denoted by reference sign P3 is incorrectly referred to. However,the correct reference destination is a pixel denoted by reference signP2. Thus, by performing ½ times scaling of the intra predictiondirection of the luma signal in the horizontal direction to be the intraprediction direction of the chroma signal, as denoted by reference sign2703, a correct intra prediction direction in the array of the chromasignals is calculated, and a pixel (a pixel neighboring thereto is alsoreferred to due to a filtering process) neighboring to the upper sidethat is the correct reference destination in the intra predictiondirection is derived.

In FIGS. 27A and 27B, although a case has been described in which apixel that is neighboring to the upper side of a prediction block isreferred to, a case may be similarly applied in which a pixel that isneighboring to the left side thereof is referred to. In the case of apixel neighboring to the left side, by performing two-times scaling ofthe intra prediction direction of a luma signal in the verticaldirection (this is the same as deriving of the direction of the intradirection and performing ½ times scaling in the vertical direction), acorrect intra prediction direction in the array of chroma signals iscalculated, and a pixel (including a pixel that is partially neighboringto the upper side) neighboring to the left side that is a correctreference destination in the intra prediction direction is derived.

Thus, in the conversion table illustrated in FIG. 15, as denoted bydotted-line arrows illustrated in FIG. 8, when the values of the lumaintra prediction mode in which reference destinations are aligned in thehorizontal direction (on the horizontal axis) are 3, 18, 10, 19, 4, 20,11, 21, 0, 22, 12, 23, 5, 24, 13, 25, and 6, by performing ½ timesscaling of such values in the horizontal direction, values of the chromaintra prediction modes in the prediction direction closest to thecalculated prediction direction are selected, and the values of thechroma intra prediction modes are respectively set to 19, 4, 20, 20, 11,11, 21, 0, 0, 0, 22, 12, 12, 23, 23, 5, and 24. Here, performing ½ timescaling of the prediction direction of the intra prediction in thehorizontal direction is the same as performing two-times scaling thereofin the vertical direction. Thus, when an intra prediction of a chromasignal is performed in a prediction direction derived by performingtwo-times scaling of each prediction direction of the luma intraprediction mode in the vertical direction or in a prediction directionneighboring thereto, a result of the prediction that is the same as orclose to that of the intra prediction of the luma signal of theprediction block located at the same position as the position of theprediction block of chroma signals is derived. Accordingly, in theconversion table illustrated in FIG. 15, as illustrated in FIG. 8, whenthe values of the luma intra prediction mode in which referencedestinations are aligned in the vertical direction (on the verticalaxis) are 26, 14, 27, 7, 28, 15, 29, 1, 30, 16, 31, 8, 32, 17, 33, and9, by performing two-times scaling of such values in the verticaldirection, values of the chroma intra prediction modes in a predictiondirection closest to the calculated prediction direction are selected,and the values of the chroma intra prediction modes are respectively setto 10, 18, 3, 26, 27, 28, 15, 1, 16, 31, 32, 33, 9, 9, 9, and 9.

On the other hand, in a case where the chroma format is 4:2:0 or 4:4:4,when the value of the chroma intra prediction mode is predicted based onthe value of the luma intra prediction mode, the intra predictiondirection of the luma signal and the intra prediction direction of thechroma signal coincide with each other, and the value of the luma intraprediction mode does not need to be converted into the value of thechroma intra prediction mode. This will be described with reference toFIGS. 28A and 28B. FIGS. 28A and 28B are diagrams that illustrate thecorrespondence relation between the prediction directions of intrapredictions of a luma signal and a chroma signal in a case where thechroma format is 4:2:0. FIG. 28A illustrates the arrangement of lumasignals and chroma signals in the case where the chroma format is 4:2:0.The chroma signals are sampled at a half ratio horizontally andvertically. An arrow, which is denoted by reference sign 2704 from apixel P4 to a pixel P5 represents the intra prediction direction of thepixel P4 of the luma signal. An arrow, denoted by reference sign 2705from a pixel P1 to a pixel P2 represents the intra prediction directionof the pixel P1 of the chroma signal. The arrow, which is denoted byreference sign 2704 from the pixel P4 to the pixel P5 and the arrow,which is denoted by reference sign 2705 from the pixel P1 to the pixelP2 are directed in the same direction, and the intra predictiondirections are the same. In this case, also in the arrangement of chromasignals illustrated in FIG. 28B, the intra prediction direction of theluma signal is, as denoted by reference sign 2706, directly the intraprediction direction of the chroma signal, and accordingly, the pixel P2that is the reference destination of the pixel P1 of the chroma signalcan be correctly referred to.

In addition, in consideration of the above-described points, in a casewhere the value of the chroma intra prediction mode is predicted, theintra prediction unit 103 predicts the value of the chroma intraprediction mode based on the value of the luma intra prediction mode ofthe prediction block located at the same position as the position of theprediction block of the chroma signal in accordance with the chromaformat. In other words, in a case where the chroma format is 4:2:0 or4:4:4, and the value of the chroma intra prediction mode is predicted,the value of the luma intra prediction mode of a prediction blocklocated at the same position as the position of the prediction block ofthe chroma signal is directly set as the value of the chroma intraprediction mode. In a case where the chroma format is 4:2:2, and thevalue of the chroma intra prediction mode is predicted, based on theconversion table illustrated in FIG. 15, the value of the chroma intraprediction mode is calculated in accordance with the value of the lumaintra prediction mode of the prediction block located at the sameposition as the position of the prediction block of the chroma signal.

In a case where the value of the syntax elementintra_chroma_pred_mode[x0][y0] is in the range of “1” to “4”, by using aconversion table illustrated in FIG. 14, on the decoding side, the valueof the chroma intra prediction mode is calculated based on a combinationof the value of the syntax element intra_chroma_pred_mode[x0][y0] andthe value of the luma intra prediction mode of the prediction blocklocated at the same position as the position of the prediction block ofthe chroma signal.

In a case where the value of the syntax elementintra_chroma_pred_mode[x0][y0] is “1”, the value of the chroma intraprediction mode takes the value of “0” or “1” in accordance with thevalue of the luma intra prediction mode of a prediction block located atthe same position as the position of the prediction block of the chromasignal.

In a case where the value of the syntax elementintra_chroma_pred_mode[x0][y0] is “2”, the value of the chroma intraprediction mode takes the value of “1” or “2” in accordance with thevalue of the luma intra prediction mode of a prediction block located atthe same position as the position of the prediction block of the chromasignal.

In a case where the value of the syntax elementintra_chroma_pred_mode[x0][y0] is “3”, the value of the chroma intraprediction mode takes the value of “2” or “3” in accordance with thevalue of the luma intra prediction mode of a prediction block located atthe same position as the position of the prediction block of the chromasignal.

In a case where the value of the syntax elementintra_chroma_pred_mode[x0][y0] is “4”, the value of the chroma intraprediction mode takes the value of “3”.

FIG. 16 is a conversion table used for calculating the value of a syntaxelement intra_chroma_pred_mode[x0][y0]relating to a chroma intraprediction mode based on the value of a chroma intra prediction mode andthe value of a luma intra prediction mode of a prediction block of lumasignals that is located at the same position as the position of aprediction block of a chroma signal, and the conversion tableillustrated in FIG. 16 corresponds to the conversion table illustratedin FIG. 14. By using the conversion table illustrated in FIG. 16, on thecoding side, the value of the syntax elementintra_chroma_pred_mode[x0][y0] is calculated.

In a case where the value of the chroma intra prediction mode is “0”,the value of the syntax element intra_chroma_pred_mode [x0][y0] takesthe value of “0” or “1” in accordance with the value of the luma intraprediction mode of a prediction block located at the same position asthe position of the prediction block of the chroma signal.

In a case where the value of the chroma intra prediction mode is “1”,the value of the syntax element intra_chroma_pred_mode[x0][y0] takes thevalue of “0”, “1”, or “2” in accordance with the value of the luma intraprediction mode of a prediction block located at the same position asthe position of the prediction block of the chroma signal.

In a case where the value of the chroma intra prediction mode is “2”,the value of the syntax element intra_chroma_pred_mode[x0][y0] takes thevalue of “0”, “2”, or “3” in accordance with the value of the luma intraprediction mode of a prediction block located at the same position asthe position of the prediction block of the chroma signal.

In a case where the value of the chroma intra prediction mode is “3”,the value of the syntax element intra_chroma_pred_mode[x0][y0] takes thevalue of “0”, “3”, or “4” in accordance with the value of the luma intraprediction mode of a prediction block located at the same position asthe position of the prediction block of the chroma signal.

In a case where the value of the chroma intra prediction mode is in therange of “4” to “33”, it is represented that the chroma intra predictionmode is predicted based on the value of the luma intra prediction modeof a prediction block located at the same position, and the value of thesyntax element intra_chroma_pred_mode[x0][y0] takes the value of “0”.However, in a case where the chroma format is 4:2:2, and the value ofthe chroma intra prediction mode is predicted, the intra prediction unit103, based on the conversion table illustrated in FIG. 15, calculatesthe value of the chroma intra prediction mode in accordance with thevalue of the luma intra prediction mode of a prediction block located atthe same position as the position of the prediction block of the chromasignal, and accordingly, the value of the chroma intra prediction modecan take any one of 4, 5, 9, 10, 11, 12, 15, 16, 18, 19, 20, 21, 22, 23,24, 26, 27, 28, 31, 32, and 33.

In order to specify a prediction block of the luma signal that islocated at the same position as the position of the prediction block ofthe chroma signal, the partition index PartIdx that specifies eachprediction block may be referred to, or the coordinates that representthe position of each prediction block may be referred to.

In addition, the number of the chroma intra prediction modes of theprediction blocks within the coding block differs in accordance with acombination of the partition mode and the chroma format supplied fromthe chroma format setting unit 101. In a case where the partition modeis the 2N.times.2N partition, regardless of the type of the chromaformat, the value of the syntax element relating to the chroma intraprediction mode of one prediction block is calculated for each codingblock.

In a case where the partition mode is the N.times.N partition, and thechroma format is 4:2:0, the value of the syntax element relating to theluma intra prediction mode of one prediction block is calculated foreach coding block. In addition, in a case where the partition mode isthe N.times.N partition, and the chroma format is 4:2:2, the values ofthe syntax elements relating to the luma intra prediction modes of twoprediction blocks are calculated for each coding block. In a case wherethe partition mode is the N.times.N partition, and the chroma format is4:4:4, the values of the syntax elements relating to the luma intraprediction modes of four prediction blocks are calculated for eachcoding block.

In a case where the prediction mode PredMode of the coding block is theinter prediction MODE_INTER, the syntax element calculating unit 124relating to the inter prediction information calculates the value of thesyntax element relating to the inter prediction information in units ofprediction blocks and supplies the calculated value of each syntaxelement to the entropy coding unit 126. In the inter predictioninformation in units of prediction blocks, information such as the interprediction mode (the L0 prediction, the L1 prediction, or bothpredictions), an index used for specifying a plurality of referencepictures, and a motion vector is included.

The entropy coding unit 126 performs entropy coding of the value of thesyntax element relating to the coding information in units of codingblocks that is supplied from the syntax element calculating unit 121relating to the coding information in units of coding blocks, the valueof the syntax element relating to the luma intra prediction mode of theprediction block of the luma signal that is supplied from the syntaxelement calculating unit 122 relating to the luma intra prediction mode,the value of the syntax element relating to the chroma intra predictionmode of the prediction block of the chroma signal that is supplied fromthe syntax element calculating unit 123 relating to the chroma intraprediction mode, and the value of the syntax element relating to theinter prediction information in units of prediction blocks that issupplied from the syntax element calculating unit 124 relating to theinter prediction information in accordance with a syntax rule set inadvance. At that time, the intra prediction mode coding control unit 125controls the sequence of the entropy coding of the luma intra predictionmode and the chroma intra prediction mode in accordance with thepartition mode and the chroma format, and the entropy coding unit 126performs the entropy coding process of the luma intra prediction modeand the chroma intra prediction mode in the sequence directed by theintra prediction mode coding control unit 125.

Hereinafter, the sequence of the entropy coding of the luma intraprediction mode and the chroma intra prediction mode at the time of theN.times.N partition, which is performed by the entropy coding unit 126controlled by the intra prediction mode coding control unit 125, will bedescribed. FIGS. 17A to 17C are diagrams that illustrate entropy codingor decoding sequences of syntax elements relating to the luma intraprediction mode and the chroma intra prediction mode at the time ofN.times.N partition according to the embodiment. FIGS. 17A, 17B, and 17Cillustrate the entropy coding and decoding sequences in a case where thechroma formats are respectively 4:2:0, 4:2:2, and 4:4:4. Here, L0, L1,L2, and L3 represent that the partition indexes PartIdx of luma signalsare syntax elements relating to the luma intra prediction modes of “0”,“1”, “2”, and “3”. In addition, C0, C1, C2, and C3 represent that thepartition indexes PartIdx of chroma signals are syntax elements relatingto the chroma intra prediction modes of the prediction blocks of “0”,“1”, “2”, and “3”

In a case where the chroma format is 4:2:0, after L0, L1, L2, and L3 arecoded, C0 is coded (C1, C2, and C3 are neither present nor coded).

In a case where the chroma format is 4:2:2, L0, L1, L2, and L3 arecoded, and subsequently, C0 and C2 are coded (C1 and C3 are neitherpresent nor coded).

In a case where the chroma format is 4:4:4, L0, L1, L2, and L3 arecoded, and subsequently, C0, C1, C2, and C3 are sequentially coded.

In other words, after the luma intra prediction modes included in thesame coding block are consecutively coded, the chroma intra predictionmodes are consecutively coded.

Next, the decoding process of coding information in units of codingblocks and prediction blocks that is performed by the second bitstreamdecoding unit 203 illustrated in FIG. 2 will be described with focusingon points relating to the intra prediction mode that is a feature of theembodiment. FIG. 13 is a block diagram that illustrates theconfiguration of the second bitstream decoding unit 203 illustrated inFIG. 2.

As illustrated in FIG. 13, the second bitstream decoding unit 203illustrated in FIG. 2 is configured by: an intra prediction modedecoding control unit 221; an entropy decoding unit 222; a codinginformation calculating unit 223 in units of coding blocks; a luma intraprediction mode calculating unit 224; a chroma intra prediction modecalculating unit 225; and an inter prediction information calculatingunit 226. Each unit configuring the second bitstream decoding unit 203performs the process according to the chroma format information suppliedfrom the chroma format managing unit 205 and performs the processaccording to the coding information such as the prediction mode and thepartition mode in units of coding blocks.

The entropy decoding unit 222 performs entropy decoding of a bitstreamincluding coding information in units of coding blocks and predictionblocks, which is supplied from the bitstream splitting unit, inaccordance with a syntax rule set in advance and derives the value ofthe syntax element relating to the coding information in units of codingblocks, the value of the syntax element relating to the luma intraprediction mode of the prediction block of luma signals, the value ofthe syntax element relating to the chroma intra prediction mode of theprediction block of chroma signals, and the value of the syntax elementrelating to the inter prediction information in units of predictionblocks. At that time, the intra prediction mode decoding control unit221 controls the sequence of the entropy decoding of the luma intraprediction mode and the chroma intra prediction mode in accordance withthe partition mode and the chroma format, and the entropy decoding unit222 performs the entropy decoding process of the luma intra predictionmode and the chroma intra prediction mode in the sequence directed bythe intra prediction mode decoding control unit 221. The intraprediction mode decoding control unit 221 is a control unit thatcorresponds to the intra prediction mode coding control unit 125disposed on the coding side and sets the decoding sequence of the intraprediction mode, which is the same as the coding sequence of the intraprediction mode set by the intra prediction mode coding control unit125, in accordance with the partition mode and the chroma format andcontrols the decoding sequence of the intra prediction mode of theentropy decoding unit 222. The entropy decoding unit 222 is a decodingunit that corresponds to the entropy coding unit 126 disposed on thecoding side and performs entropy decoding in accordance with the samerule as the syntax rule used by the entropy coding unit 126. In otherwords, the decoding process of the intra prediction mode is performed inthe same sequence as the coding sequence illustrated in FIGS. 17A to17C. In other words, after the luma intra prediction modes belonging tothe same coding block are consecutively decoded, the chroma intraprediction modes are sequentially decoded.

The value of the syntax element relating to the coding information inunits of coding blocks, which has been acquired by being decoded, issupplied to the coding information calculating unit 223 in units ofcoding blocks, the value of the syntax element relating to the lumaintra prediction mode of the prediction block of luma signals issupplied to the luma intra prediction mode calculating unit 224, thevalue of the syntax element relating to the chroma intra prediction modeof the prediction block of chroma signals is supplied to the chromaintra prediction mode calculating unit 225, and the value of the syntaxelement relating to the inter prediction information in units ofprediction blocks is supplied to the inter prediction informationcalculating unit 226.

The coding information calculating unit 223 in units of coding blockscalculates the coding information in units of coding blocks based on thesupplied value of the syntax element relating to the coding informationin units of the coding blocks and supplies the calculated codinginformation to the intra prediction unit 206 or the inter predictionunit 207 through the switch 212.

The coding information calculating unit 223 in units of coding blocks isa coding information calculating unit that corresponds to the syntaxelement calculating unit 121 relating to the coding information in unitsof coding blocks disposed on the coding side and performs calculation inaccordance with the same semantics rule. The values relating to theprediction mode PredMode used for determining either the intraprediction MODE_INTRA or the inter prediction MODE_INTER of the codingblock and the partition mode PartMode used for determining the shape ofthe prediction block are calculated by the coding informationcalculating unit 223 in units of coding blocks.

In a case where the prediction mode PredMode of the coding block that iscalculated by the coding information calculating unit 223 in units ofcoding blocks is the intra prediction MODE_INTRA, the luma intraprediction mode calculating unit 224 calculates the luma intraprediction mode of the prediction block of luma signals based on thesupplied value of the syntax element relating to the luma intraprediction mode of the prediction block of luma signals, supplies thecalculated luma intra prediction mode to the chroma intra predictionmode calculating unit 225, and supplies the calculated luma intraprediction mode to the intra prediction unit 206 through the switch 212.The luma intra prediction mode calculating unit 224 is a codinginformation calculating unit that corresponds to the syntax elementcalculating unit 122 relating to the luma intra prediction mode disposedon the coding side and performs calculation in accordance with the samesemantics rule. As the syntax elements relating to the luma intraprediction mode, there are a syntax elementprev_intra_luma_pred_flag[x0][y0] that is a flag representing whether ornot a prediction can be made based on the luma intra prediction mode ofa neighboring block, a syntax element mpm_idx[x0][y0] that is an indexindicating a prediction block of a prediction source, and a syntaxelement rem_intra_luma_pred_mode[x0][y0] that represents the luma intraprediction mode in units of prediction blocks. In the calculation of theluma intra prediction mode, the correlation with the luma intraprediction mode of a neighboring block stored in the coding informationstoring memory 210 is used. In a case where the prediction can be madebased on the luma intra prediction mode of the neighboring block, thesyntax element prev_intra_luma_pred_flag[x0][y0], which is a flagrepresenting the use of the value, is “1” (true), and the luma intraprediction mode of the neighboring prediction block that is directedbased on the syntax element mpm_idx[x0][y0] that is an index indicatingthe prediction block of a prediction source is set as the luma intraprediction mode of the prediction mode. On the other hand, in a casewhere the syntax element prev_intra_luma_pred_flag[x0][y0] is “0”(false), the luma intra prediction mode is not predicted based on theneighboring prediction block, but the luma intra prediction mode iscalculated based on the value of the syntax elementrem_intra_lumapred_mode[x0][y0] that represents the decoded luma intraprediction mode.

The number of luma intra prediction modes of the prediction block withinthe coding block differs in accordance with the partition mode. Thus, ina case where the partition mode is the 2N.times.2N partition, the valuesof the luma intra prediction mode of one set of prediction blocks arecalculated for each coding block. On the other hand, in a case where thepartition mode is the N.times.N partition, the values of the luma intraprediction modes of four sets of prediction blocks are calculated foreach coding block.

The chroma intra prediction mode calculating unit 225, in a case wherethe prediction mode PredMode of the coding block, which is calculated bythe coding information calculating unit 223 in units of coding blocks,is the intra prediction MODE_INTRA, calculates the value of the chromaintra prediction mode based on the supplied value of the syntax elementintra_chroma_pred_mode[x0][y0] relating to the chroma intra predictionmode of the prediction block of chroma signals and the value of the lumaintra prediction mode that is supplied from the luma intra predictionmode calculating unit and supplies the calculated value of the chromaintra prediction mode to the intra prediction unit 206 through theswitch 212. The chroma intra prediction mode calculating unit 225 is acoding information calculating unit that corresponds to the syntaxelement calculating unit 123 relating to the chroma intra predictionmode disposed on the coding side and performs calculation in accordancewith the same semantics rule. In the calculation of the value of thechroma intra prediction mode, the correlation with the luma intraprediction mode of the prediction block of luma signals that is locatedat the same position as the position of the prediction block of chromasignals is used. Thus, in a case where it is determined that a chromaintra prediction mode can be predicted based on the luma intraprediction mode of the prediction block of luma signals that is locatedat the same position as the position of the prediction block of chromasignals on the coding side, the value of the chroma intra predictionmode is predicted based on the value of the luma intra prediction mode.On the other hand, in a case where it is determined that an independentvalue is preferably set to the chroma intra prediction mode rather thanmaking a prediction based on the luma intra prediction mode, a structureis used in which any one of “0” (horizontal direction), “1” (horizontaldirection), “2” (average value), and “3” (inclination of 45 degrees),which are representative intra prediction modes, is set to the chromaintra prediction mode. As a result, the code amount is reduced.

FIG. 14 is a conversion table used for calculating the value of thechroma intra prediction mode based on the value of the syntax elementintra_chroma_pred_mode[x0][y0] and the value of the luma intraprediction mode of the prediction block located at the same position asthe position of the prediction block of chroma signals. By using thisconversion table, the value of the chroma intra prediction mode iscalculated. As presented in the description of the coding side, in acase where the value of the syntax element intra_chroma_pred_mode[x0][y0] is “0”, the value of the chroma intra prediction mode ispredicted in accordance with the chroma format based on the value of theluma intra prediction mode of the prediction block located at the sameposition as the position of the prediction block of chroma signals. In acase where the chroma format is 4:2:0 or 4:4:4, and the value of thesyntax element intra_chroma_pred_mode[x0][y0] is “0”, the value of theluma intra prediction mode of the prediction block located at the sameposition as the position of the prediction block of chroma signals isdirectly set as the value of the chroma intra prediction mode. In a casewhere the chroma format is 4:2:2 and the value of the syntax elementintra_chroma_pred_mode[x0][y0] is “0”, based on the conversion tableillustrated in FIG. 15, the value of the chroma intra prediction mode iscalculated based on the value of the luma intra prediction mode of theprediction block located at the same position as the position of theprediction block of chroma signals. FIG. 15 is a conversion table usedfor calculating the value of the chroma intra prediction mode based onthe value of the luma intra prediction mode of the prediction blocklocated at the same position as the position of the prediction block ofchroma signals in a case where the chroma format is 4:2:2 that isdefined in this example.

In a case where the prediction mode PredMode of the coding block is theinter prediction MODE_INTER, the inter prediction informationcalculating unit 226 calculates the inter prediction information basedon the value of the syntax element relating to the inter predictioninformation in units of prediction blocks and supplies the calculatedvalue of the inter prediction information to the inter prediction unit207 through the switch 212. The inter prediction information calculatingunit 226 is a coding information calculating unit that corresponds tothe syntax element calculating unit 124 relating to the inter predictioninformation disposed on the coding side and performs calculation inaccordance with the same semantics rule. In the calculated interprediction information in units of prediction blocks, information suchas the inter prediction mode (the L0 prediction, the L1 prediction, orboth predictions), an index used for specifying a plurality of referencepictures, and a motion vector is included.

Next, the syntax rule used in this example will be described withfocusing on points relating to the intra prediction mode that is afeature of the embodiment. FIG. 18 is an example of a syntax rule usedfor coding and decoding coding information of a prediction block that isused by the coding-side entropy coding unit 126 and the decoding-sideentropy decoding unit 222. In FIGS. 18, x0 and y0 are coordinates thatrepresent the position of the prediction block of luma signals. FIG. 18illustrates the process of the entropy coding or entropy decoding of thesyntax element relating to the luma intra prediction mode in units ofone set of prediction blocks in a case where the prediction modePredMode is the intra prediction MODE_INTRA, and an IntraChroma flag is“0” (false) in units of prediction blocks. The IntraChroma is “1” (true)when information relating to the chroma intra prediction mode is codedin an intra prediction but is “0” (false) at any other time. In a casewhere the prediction mode PredMode is the intra prediction MODE_INTRAand the IntraChroma flag is “0” (false), entropy coding or entropydecoding of the syntax element prev_intra_luma_pred_flag[x0][y0] isperformed. On the other hand, in a case where the syntax elementprev_intra_luma_pred_flag[x0][y0] is “1” (true), entropy coding orentropy decoding of the syntax element mpm_idx[x0][y0] is performed. Ina case where the syntax element prev_intra_luma_pred_flag[x0][y0] is “0”(false), entropy coding or entropy decoding of the syntax elementrem_intra_luma_pred_mode[x0][y0] is performed. In a case where thepartition mode is the 2N.times.2N partition, when entropy coding orentropy decoding of the syntax element relating to one set of luma intraprediction modes is performed for the coding block, the IntraChroma flagis “0” (false), and this syntax rule is applied. In a case where thepartition mode is the N.times.N partition, every time when entropycoding or entropy decoding of the syntax elements P0, P1, P2, and P3relating to the luma intra prediction mode illustrated in FIGS. 17A to17C is performed, the IntraChroma flag is “0” (false), and this syntaxrule is applied.

On the other hand, in a case where the prediction mode is the intraprediction MODE_INTRA and the IntraChroma flag is “1” (true), entropycoding or entropy decoding of the syntax elementintra_chroma_pred_mode[x0][y0] relating to the chroma intra predictionmode is illustrated to be performed. In a case where the partition modeis the 2N.times.2N partition, when entropy coding or entropy decoding ofthe syntax element relating to one set of chroma intra prediction modesis performed for the coding block, the IntraChroma flag is “1” (true),and the rule of the syntax is applied. In a case where the partitionmode is the N.times.N partition, in accordance with the chroma format,every time when entropy coding or entropy decoding of syntax elementsC0, C1, C2, and C3 relating to the chroma intra prediction modeillustrated in FIGS. 17A to 17C is performed, the IntraChroma flag is“1” (true), and this syntax rule is applied.

Next, an example of a syntax rule other than the syntax rule representedin FIG. 18 will be described. FIG. 19 is another example of the syntaxrule, which is different from the example illustrated in FIG. 18, usedfor coding and decoding coding information of a prediction block that isused by the coding-side entropy coding unit 126 and the decoding-sideentropy decoding unit 222. In FIGS. 19, x0 and y0 are coordinates thatrepresent the position of the prediction block of luma signals. FIG. 19illustrates the process of the entropy coding or entropy decoding of thesyntax element relating to the luma intra prediction mode in units ofone set of prediction blocks, which is performed in units of predictionblocks in a case where the prediction mode PredMode is the intraprediction (MODE_INTRA). In a case where the prediction mode (PredMode)is the intra prediction MODE_INTRA, entropy coding or entropy decodingof the syntax element prev_intra_luma_pred_flag[x0][y0] is performed. Onthe other hand, in a case where the syntax elementprev_intra_luma_pred_flag[x0][y0] is “1” (true), entropy coding orentropy decoding of the syntax element mpm_idx[x0][y0] is performed. Ina case where the syntax element prev_intra_luma_pred_flag[x0][y0] is “0”(false), entropy coding or entropy decoding of the syntax elementrem_intra_luma_pred_mode[x0][y0] is performed. In a case where thepartition mode is the 2N.times.2N partition, when entropy coding orentropy decoding of the syntax element relating to one set of luma intraprediction modes is performed for the coding block, this syntax rule isapplied. In a case where the partition mode is the N.times.N partition,every time when entropy coding or entropy decoding of the syntaxelements P0, P1, P2, and P3 relating to the luma intra prediction modeillustrated in FIGS. 17A to 17C is performed, this syntax rule isapplied.

In addition, in a case where the prediction mode PredMode is the intraprediction MODE_INTRA, entropy coding or entropy decoding of the syntaxelements relating to 0 to 4 chroma intra prediction modes is illustratedto be performed in accordance with the partition mode PartMode, thechroma format ChromaArrayType, and the partition index PartIdx. Thechroma format ChromaArrayType is a variable that represents the chromaformat, “0” represents monochrome (basically, although a mode in whichluma signals and chroma signals are independently coded at 4:4:4 isincluded, such a case is regarded as the monochrome in this example),“1” represents 4:2:0, “2” represents 4:2:2, and “3” represents 4:4:4.

In a case where the prediction mode PredMode is the intra predictionMODE_INTRA, the partition mode PartMode is the 2N.times.2N partitionPART_2N.times.2N and the chroma format ChromaArrayType is not themonochrome (0), entropy coding or entropy decoding of the syntax elementintra_chroma_pred_mode[x0][y0] relating to the chroma intra predictionmode in units of prediction blocks is illustrated to be performed. In acase where the partition mode is the 2N.times.2N partition, when entropycoding or entropy decoding of the syntax element relating to one set ofthe luma intra prediction modes is performed for the coding block afterthe entropy coding or entropy decoding of the syntax element relating toone set of luma intra prediction modes is performed for the codingblock, this syntax rule is applied.

On the other hand, when the prediction mode PredMode is the intraprediction MODE_INTRA, the partition mode PartMode is the N.times.Npartition PART_N.times.N, and the partition index PartIdx is “3”, asyntax rule described below is applied. First, in a case where thechroma format ChromaArrayType is not the monochrome (0), in other words,in a case where the chroma format is 4:2:0, 4:2:2, or 4:4:4, entropycoding or entropy decoding of the syntax elementintra_chroma_pred_mode[x1][y1] relating to the chroma intra predictionmode of which the partition index PartIdx is “0” is performed, andsubsequently, in a case where the chroma format ChromaArrayType is 4:4:4(3), entropy coding or entropy decoding of the syntax elementintra_chroma_pred_mode[x0][y1] relating to the chroma intra predictionmode of which the partition index PartIdx is “1” is performed.Subsequently, in a case where the chroma format ChromaArrayType is 4:2:2(2) or 4:4:4 (3), entropy coding or entropy decoding of the syntaxelement intra_chroma_pred_mode[x1][y0] relating to the chroma intraprediction mode of which the partition index PartIdx is “2” isperformed, and subsequently, in a case where the chroma formatChromaArrayType is 4:4:4 (3), entropy coding or entropy decoding of thesyntax element intra_chroma_pred_mode[x0][y0] relating to the chromaintra prediction mode of which the partition index PartIdx is “3” isillustrated to be performed. In a case where the partition mode is theN.times.N partition, when entropy coding or entropy decoding of thesyntax elements C0, C1, C2, and C3 relating to the chroma intraprediction modes of which the number corresponds to the chroma format isperformed after the entropy coding or entropy decoding of the syntaxelement P3 relating to the luma intra prediction mode of which thepartition index PartIdx is “3” illustrated in FIGS. 17A to 17C isperformed, this syntax rule is applied.

Next, the processing sequence of the coding process of codinginformation in units of coding blocks and prediction blocks that isperformed by the second bitstream constructing unit 113 illustrated inFIG. 11 will be described with focusing on points relating to the intraprediction mode that is a feature of the embodiment. FIG. 20 is aflowchart that illustrates the processing sequence of the coding processin units of coding blocks and prediction blocks that is performed by thesecond bitstream constructing unit 113 illustrated in FIG. 1.

First, on the coding side, the value of the syntax element relating tocoding information including the prediction mode of the coding block,the partition mode, and the like is calculated by the syntax elementcalculating unit 121 relating to the coding information in units ofcoding blocks, and entropy coding of the calculated value of the syntaxelement is performed by the entropy coding unit 126 in step S1001.Subsequently, in a case where the prediction mode PredMode of the codingblock is not the intra prediction MODE_INTRA (No in step S1002), theprocess proceeds to step S1017, the value of the syntax element relatingto inter information is calculated for each prediction block inaccordance with the partition mode by the syntax element calculatingunit 124 relating to the inter prediction information, entropy coding ofthe calculated value of the syntax element is performed by the entropycoding unit 126 in step S1017, and this coding process ends. In a casewhere the prediction mode PredMode of the coding block is the intraprediction MODE_INTRA (Yes in step S1002), the process proceeds to acoding process of the intra prediction mode of step S1003 and subsequentsteps.

Subsequently, in a case where the prediction mode of the coding block isthe intra prediction, a coding process of the luma intra prediction modeof the prediction block, of which the partition index PartIdx is “0”, ofluma signals is performed by the syntax element calculating unit 122relating to the luma intra prediction mode and the entropy coding unit126 in step S1003.

Here, the sequence of the coding process of the luma intra predictionmode of the prediction block of luma signals, which is performed by thesyntax element calculating unit 122 relating to the luma intraprediction mode and the entropy coding unit 126, will be described byreferring to a flowchart illustrated in FIG. 21. FIG. 21 is a flowchartthat illustrates the sequence of the coding process of the luma intraprediction mode of the prediction block of luma signals, which isperformed by the syntax element calculating unit 122 relating to theluma intra prediction mode and the entropy coding unit 126. First, thevalue of each syntax element relating to the luma intra prediction modeof the prediction block of luma signals is calculated by the syntaxelement calculating unit 122 relating to the luma intra prediction modein step S1101. At this time, the value of the luma intra prediction modeis compared with the luma intra prediction mode of a neighboring block.In a case where a prediction block having the same value is present, thevalue of the syntax element prev_intra_luma_pred_flag[x0][y0] is set to“1” (true), and a value used for specifying a reference destination isset to the syntax element mpm_idx[x0][y0] that is an index indicatingthe prediction block of a prediction source. On the other hand, in acase where there is no prediction block having the same value, the valueof the syntax element prev_intra_luma_pred_flag[x0][y0] is set to “0”(false), and a value used for specifying the luma intra prediction modeis set to the syntax element rem_intra_luma_pred_mode[x0][y0] thatrepresents the luma intra prediction mode. Subsequently, entropy codingof the value of each syntax element relating to the luma intraprediction mode of the prediction block of luma signals is performed bythe entropy coding unit 126 in step S1102, and this coding process ends.The sequence of the coding process illustrated in FIG. 21 is thesequence of a common coding process that is used not only in step S1003illustrated in FIG. 20 but also in steps S1005, S1006, and S1007.

Again, referring back to FIG. 20, subsequently, in a case where thepartition mode of the coding block is not the N.times.N partition, inother words, the partition mode is the 2N.times.2N (No in step S1004),since only a prediction block of which the partition index PartIdx is“0” is present, and there is no more intra prediction mode of theprediction block of luma signals to be coded, the process of steps S1005to S1007 is skipped, and the process proceeds to the coding process ofthe intra prediction mode of the prediction block of chroma signals ofstep S1008 and subsequent steps.

On the other hand, in a case where the partition mode of the codingblock is the N.times.N partition (Yes in step S1004), the processproceeds to the coding process of the intra prediction mode of theprediction block of luma signals of which the partition index PartIdx islarger than “0”. First, in the sequence of the coding processingillustrated in FIG. 21, the coding process of the luma intra predictionmode of the prediction block, of which the partition index PartIdx is“1”, of luma signals is performed in step S1005. Subsequently, in thesequence of the coding process illustrated in FIG. 21, the codingprocess of the luma intra prediction mode of the prediction block, ofwhich the partition index PartIdx is “2”, of luma signals is performedin step S1006. Subsequently, in the sequence of the coding processillustrated in FIG. 21, the coding process of the luma intra predictionmode of the prediction block, of which the partition index PartIdx is“3”, of luma signals is performed in step S1007.

Subsequently, in a case where the chroma format is 4:2:0, 4:2:2, or4:4:4 (Yes in step S1008), the coding process of the chroma intraprediction mode of the prediction block, of which the partition indexPartIdx is “0”, of chroma signals is performed by the syntax elementcalculating unit 123 relating to the chroma intra prediction mode andthe entropy coding unit 126 in step S1009. In addition, in a case wherethe chroma format is not any one of 4:2:0, 4:2:2, and 4:4:4, in otherwords, in a case where the chroma format is the monochrome (No in stepS1008), since there is no prediction block of chroma signals, step S1009and the subsequent steps are skipped, and this coding process ends.

Here, the sequence of the coding process of the chroma intra predictionmode of the prediction block of chroma signals that is performed by thesyntax element calculating unit 123 relating to the chroma intraprediction mode and the entropy coding unit 126 will be described byreferring to a flowchart illustrated in FIG. 22. FIG. 22 is a flowchartthat illustrates the sequence of the coding process of the chroma intraprediction mode of the prediction block of chroma signals, which isperformed by the syntax element calculating unit 123 relating to thechroma intra prediction mode and the entropy coding unit 126. First, thevalue of each syntax element relating to the chroma intra predictionmode of the prediction block of chroma signals is calculated by thesyntax element calculating unit 123 relating to the chroma intraprediction mode in step S1201. At this time, the value of the syntaxelement intra_chroma_pred_mode[x0][y0] relating to the chroma intraprediction mode is calculated based on the value of the chroma intraprediction mode and the value of the luma intra prediction mode of theprediction block located at the same position as the position of theprediction block of chroma signals by using the conversion tableillustrated in FIG. 16. Subsequently, entropy coding of the value ofeach syntax element relating to the chroma intra prediction mode of theprediction block of chroma signals is performed by the entropy codingunit 126 in step S1202, and this coding process ends. The coding processsequence illustrated in FIG. 22 is the sequence of a common codingprocess that is used not only in step S1009 illustrated in FIG. 20 butalso in steps S1012, S1014, and S1016.

Again, referring back to FIG. 20, subsequently, in a case where thepartition mode of the coding block is not the N.times.N partition, inother words, the partition mode is the 2N.times.2N (No in step S1010),since only a prediction block of which the partition index PartIdx is“0” is present, and there is no more intra prediction mode of theprediction block of chroma signals to be coded, the process of stepS1011 and the subsequent steps is skipped, and this coding process ends.

Subsequently, in a case where the chroma format is 4:4:4 (Yes in stepS1011), in the sequence of the coding process illustrated in FIG. 22, acoding process of the chroma intra prediction mode of the predictionblock, of which the partition index PartIdx is “1”, of chroma signals isperformed in step S1012. On the other hand, in a case where the chromaformat is not 4:4:4, in other words, in a case where the chroma formatis 4:2:0 or 4:2:2 (No in step S1011), since there is no predictionblock, of which the partition index PartIdx is “1”, of chroma signals,step S1012 is skipped, and the process proceeds to the next step S1013.

Subsequently, in a case where the chroma format is 4:2:2 or 4:4:4 (Yesin step 1013), in the sequence of the coding process illustrated in FIG.22, the coding process of the chroma intra prediction mode of theprediction block, of which the partition index PartIdx is “2”, of chromasignals is performed in step S1014. In addition, in a case where thechroma format is neither 4:2:2 nor 4:4:4, in other words, in a casewhere the chroma format is 4:2:0 (No in step S1013), since there is noprediction block of chroma signals of which the partition index PartIdxis “2”, step S1014 is skipped, and the process proceeds to the next stepS1015.

Subsequently, in a case where the chroma format is 4:4:4 (Yes in stepS1015), in the sequence of the coding process illustrated in FIG. 22,the coding process of the chroma intra prediction mode of the predictionblock, of which the partition index PartIdx is “3”, of chroma signals isperformed in step S1016, and this coding process ends. In addition, in acase where the chroma format is other than 4:4:4, in other words, thechroma format is 4:2:0 or 4:2:2 (No in step S1015), since there is noprediction block of chroma signals of which the partition index PartIdxis “3”, step S1016 is skipped, and this coding process ends.

According to this coding process, in the sequence illustrated in FIGS.17A to 17C, after luma intra prediction modes belonging to the samecoding block are consecutively coded, the chroma intra prediction modesare consecutively coded. Thus, when the chroma intra prediction mode iscalculated on the decoding side, the calculation process is performed byreferring to the luma intra prediction mode of the prediction block ofluma signals that is located at the same position as the position of theprediction block of chroma signals. Accordingly, by referring to theluma intra prediction mode, the coding efficiency of the chroma intraprediction mode can be improved. In addition, according to this codingprocess, when the value of the chroma intra prediction mode is predictedbased on the value of the luma intra prediction mode, by changing themethod of deriving the chroma intra prediction mode in accordance withthe chroma format, the intra prediction can be made in a predictiondirection that is appropriate in accordance with the chroma format,whereby the coding efficiency can be improved. More specifically, in acase where the chroma format is 4:2:0 or 4:4:4, the value of the lumaintra prediction mode is set as the value of the chroma intra predictionmode, and, in a case where the chroma format is 4:2:2, the value of theluma intra prediction mode is converted into the value of the chromaintra prediction mode by using the conversion table illustrated in FIG.15, and the intra prediction is made in accordance with the value of thechroma intra prediction mode. Accordingly, the intra prediction can bemade in an appropriate prediction direction, and the coding efficiencyrelating to a residual signal is improved, whereby the whole codingefficiency can be improved.

Next, the processing sequence of the decoding process of codinginformation in units of coding blocks and prediction blocks that isperformed by the second bitstream decoding unit 203 illustrated in FIG.2 will be described with focusing on points relating to the intraprediction mode that is a feature of the embodiment. FIG. 23 is aflowchart that illustrates the processing sequence of the decodingprocess in units of coding blocks and prediction blocks that isperformed by the second bitstream decoding unit 203 illustrated in FIG.2.

First, on the decoding side, the value of the syntax element relating tocoding information including the prediction mode of the coding block,the partition mode, and the like is derived by performing entropydecoding the bitstream using the entropy decoding unit 222, and thevalue of the coding information including the prediction mode of thecoding block, the partition mode, and the like is calculated based onthe value of each syntax element decoded by the coding informationcalculating unit 223 in units of coding blocks in step S2001.Subsequently, in a case where the prediction mode PredMode of the codingblock is not the intra prediction MODE_INTRA (No in step S2002), theprocess proceeds to step S2017, the value of the syntax element relatingto inter information is acquired for each prediction block in accordancewith the partition mode by performing entropy decoding using the entropydecoding unit 222, the value of the inter information is calculated foreach prediction block in accordance with the partition mode by the interprediction information calculating unit 226 in step S2017, and thisdecoding process ends. In a case where the prediction mode PredMode ofthe coding block is the intra prediction MODE_INTRA (Yes in step S2002),the process proceeds to a decoding process of the intra prediction modeof step S2003 and subsequent steps.

Subsequently, in a case where the prediction mode of the coding block isthe intra prediction, a decoding process of the luma intra predictionmode of the prediction block, of which the partition index PartIdx of is“0”, of luma signals is performed by the entropy decoding unit 222 andthe luma intra prediction mode calculating unit 224 in step S2003.

Here, the sequence of the decoding process of the luma intra predictionmode of the prediction block of luma signals, which is performed by theentropy decoding unit 222 and the luma intra prediction mode calculatingunit 224, will be described by referring to a flowchart illustrated inFIG. 24. FIG. 24 is a flowchart that illustrates the sequence of thedecoding process of the luma intra prediction mode of the predictionblock of luma signals, which is performed by the entropy decoding unit222 and the luma intra prediction mode calculating unit 224. First,entropy decoding of the bitstream is performed by the entropy decodingunit 222, whereby the value of each syntax element relating to the lumaintra prediction mode of the prediction block of luma signals is derivedin step S2101. Subsequently, the value of the luma intra prediction modeof the prediction block of luma signals is calculated based on the valueof each decoded syntax element decoded in step S2101 by the luma intraprediction mode calculating unit 224 of the luma intra prediction modein step S2102. At this time, in a case where the value of the syntaxelement prev_intra_luma_pred_flag[x0][y0] is “1” (true), the luma intraprediction mode of the neighboring prediction block indicated by thesyntax element mpm_idx[x0][y0] that is an index indicating theprediction block of a prediction source is set as the luma intraprediction mode of the prediction mode. On the other hand, in a casewhere the value of the syntax element prev_intra_luma_pred_flag[x0][y0]is “0” (false), the luma intra prediction mode is calculated based onthe value of the syntax element rem_intra_luma_pred_mode[x0][y0] thatrepresents the luma intra prediction mode, and this decoding processends. The sequence of the decoding process illustrated in FIG. 24 is thesequence of a common decoding process that is used not only in stepS2003 illustrated in FIG. 23 but also in steps S2005, S2006, and S2007.

Again, referring back to FIG. 23, subsequently, in a case where thepartition mode of the coding block is not the N.times.N partition, inother words, the partition mode is the 2N.times.2N (No in step S2004),since only a prediction block of which the partition index PartIdx is“0” is present, and there is no more intra prediction mode to bedecoded, the process of steps S2005 to S2007 is skipped, and the processproceeds to the decoding process of the intra prediction mode of theprediction block of chroma signals of step S2008 and subsequent steps.

On the other hand, in a case where the partition mode of the codingblock is the N.times.N partition (Yes in step S2004), the processproceeds to the decoding process of the intra prediction mode of theprediction block of which the partition index PartIdx is larger than“0”. First, in the sequence of the decoding process illustrated in FIG.24, the decoding process of the luma intra prediction mode of theprediction block, of which the partition index PartIdx is “1”, of lumasignals is performed in step S2005. Subsequently, in the processingsequence illustrated in FIG. 24, the decoding process of the luma intraprediction mode of the prediction block, of which the partition indexPartIdx is “2”, of luma signals is performed in step S2006.Subsequently, in the processing sequence illustrated in FIG. 24, thedecoding process of the luma intra prediction mode of the predictionblock, of which the partition index PartIdx is “3”, of luma signals isperformed in step S2007.

Subsequently, in a case where the chroma format is 4:2:0, 4:2:2, or4:4:4 (Yes in step S2008), the decoding process of the chroma intraprediction mode of the prediction block, of which the partition indexPartIdx is “0”, of chroma signals is performed by the entropy decodingunit 222 and the chroma intra prediction mode calculating unit 225 instep S2009. In addition, in a case where the chroma format is not anyone of 4:2:0, 4:2:2, and 4:4:4, in other words, in a case where thechroma format is the monochrome (No in step S2008), since there is noprediction block of chroma signals, step S2009 and the subsequent stepsare skipped, and this decoding process ends.

Here, the sequence of the decoding process of the chroma intraprediction mode of the prediction block of chroma signals that isperformed by the entropy decoding unit 222 and the chroma intraprediction mode calculating unit 225 will be described by referring to aflowchart illustrated in FIG. 25. FIG. 25 is a flowchart thatillustrates the sequence of the decoding process of the chroma intraprediction mode of the prediction block of chroma signals, which isperformed by the entropy decoding unit 222 and the chroma intraprediction mode calculating unit 225. First, the value of the syntaxelement intra_chroma_pred_mode[x0][y0] relating to the chroma intraprediction mode of the prediction block of chroma signals is calculatedby performing entropy decoding the bitstream using the entropy decodingunit 222 in step S2201. Subsequently, the value of the chroma intraprediction mode of the prediction block of chroma signals is calculatedby the chroma intra prediction mode calculating unit 225 in step S2202.Here, the sequence of the process of calculating the chroma intraprediction mode of the prediction block of chroma signals that isperformed by the chroma intra prediction mode calculating unit 225 willbe described by referring to a flowchart illustrated in FIG. 26. FIG. 26is a flowchart that illustrates the sequence of the process ofcalculating the chroma intra prediction mode that is performed in stepS2202 illustrated in FIG. 25. First, it is determined whether or not thevalue of the syntax element intra_chroma_pred_mode[x0][y0] relating tothe chroma intra prediction mode of the prediction block of chromasignals is “0” in step S2301. In a case where the value of the syntaxelement is “0” (Yes in step S2301), the process proceeds to step S2302.In a case where the chroma format is 4:2:0 or 4:4:4 (Yes in step S2302),the value of the luma intra prediction mode of the prediction blocklocated at the same position as the position of the prediction block ofchroma signals is directly set as the value of the chroma intraprediction mode in step S2303, and this calculation process ends. On theother hand, in a case where the chroma format is not 4:2:0 or 4:4:4, inother words, in a case where the chroma format is 4:2:2 (No in stepS2302), by using the conversion table illustrated in FIG. 15, the valueof the chroma intra prediction mode is calculated based on the value ofthe luma intra prediction mode of the prediction block located at thesame position as the position of the prediction block of chroma signalsin step S2304, and this calculation process ends. On the other hand, ina case where the value of the syntax elementintra_chroma_pred_mode[x0][y0] is other than “0” (No in step S2301), byusing the conversion table illustrated in FIG. 14, the value of the lumaintra prediction mode is converted into the value of the chroma intraprediction mode in step S2305, and this calculation process ends. Atthis time, the value of the syntax element is calculated based on thevalue of the syntax element intra_chroma_pred_mode[x0][y0] relating tothe chroma intra prediction mode decoded in step S2201 and the value ofthe luma intra prediction mode of the prediction block located at thesame position as the position of the prediction block of chroma signalsby using the conversion table illustrated in FIG. 14, and thiscalculation process ends. The sequence of the decoding processillustrated in FIG. 25 is the sequence of a common decoding process thatis used not only in step S2009 illustrated in FIG. 23 but also in stepsS2012, S2014, and S2016.

Again, referring back to FIG. 23, subsequently, in a case where thepartition mode of the coding block is not the N.times.N partition, inother words, the partition mode is the 2N.times.2N (No in step S2010),since only a prediction block of which the partition index PartIdx is“0” is present, and there is no more intra prediction mode of theprediction block of chroma signals to be decoded, the process of stepS2011 and subsequent steps is skipped, and this decoding process ends.

Subsequently, in a case where the chroma format is 4:4:4 (Yes in stepS2011), in the processing sequence illustrated in FIG. 25, the decodingprocess of the chroma intra prediction mode of the prediction block, ofwhich the partition index PartIdx is “1”, of chroma signals is performedin step S2012. In addition, in a case where the chroma format is not4:4:4, in other words, in a case where the chroma format is 4:2:0 or4:2:2 (No in step S2011), since there is no prediction block, of whichthe partition index PartIdx is “1”, of chroma signals, step S2012 isskipped, and the process proceeds to the next step S2013.

Subsequently, in a case where the chroma format is 4:2:2 or 4:4:4 (Yesin step S2013), in the processing sequence illustrated in FIG. 25, thedecoding process of the chroma intra prediction mode of the predictionblock, of which the partition index PartIdx is “2”, of chroma signals isperformed in step S2014. In addition, in a case where the chroma formatis neither 4:2:2 nor 4:4:4, in other words, in a case where the chromaformat is 4:2:0 (No in step S2013), since there is no prediction block,of which the partition index PartIdx is “2”, of chroma signals, stepS2014 is skipped, and the process proceeds to the next step S2015.

Subsequently, in a case where the chroma format is 4:4:4 (Yes in stepS2015), in the processing sequence illustrated in FIG. 25, the decodingprocess of the chroma intra prediction mode of the prediction block, ofwhich the partition index PartIdx is “3”, of chroma signals is performedin step S2016, and this decoding process ends. In addition, in a casewhere the chroma format is other than 4:4:4, in other words, in a casewhere the chroma format is 4:2:0 or 4:2:2 (No in step S2015), sincethere is no prediction block, of which the partition index PartIdx is“3”, of chroma signals, step S2016 is skipped, and this decoding processends.

According to this decoding process, in the sequence illustrated in FIGS.17A to 17C, after luma intra prediction modes belonging to the samecoding block are consecutively coded, the chroma intra prediction modesare consecutively decoded. Thus, when the chroma intra prediction modeis calculated, the calculation process is performed by referring to theluma intra prediction mode of the prediction block of luma signals thatis located at the same position as the position of the prediction blockof chroma signals. Accordingly, by referring to the luma intraprediction mode, the coding efficiency of the chroma intra predictionmode can be improved. In addition, according to this decoding process,when the value of the chroma intra prediction mode is predicted based onthe value of the luma intra prediction mode, by changing the method ofderiving the chroma intra prediction mode in accordance with the chromaformat, the intra prediction can be made in a prediction direction thatis appropriate in accordance with the chroma format, whereby the codingefficiency can be improved. More specifically, in a case where thechroma format is 4:2:0 or 4:4:4, the value of the luma intra predictionmode is set as the value of the chroma intra prediction mode, and, in acase where the chroma format is 4:2:2, the value of the luma intraprediction mode is converted into the value of the chroma intraprediction mode by using the conversion table illustrated in FIG. 15,and the intra prediction is made in accordance with the value of thechroma intra prediction mode. Accordingly, the intra prediction can bemade in an appropriate prediction direction, and the coding efficiencyrelating to a residual signal is improved, whereby the whole codingefficiency can be improved.

As picture coding devices according to still another aspect of thepresent invention, there are following devices.

There is provided a picture coding device that performs intra predictioncoding of a picture signal including a luma signal and a chroma signalin units of blocks and codes information relating to an intra predictionmode. The picture coding device includes: a luma signal intra predictionunit 103 that, when an intra prediction of the picture signal is made inunits of prediction blocks, sets a prediction block of luma signals andpredicts a luma signal based on a coded neighboring block of the lumasignals in accordance with a luma intra prediction mode; a chroma signalintra prediction unit 103 that sets a prediction block of chroma signalsand predicts a chroma signal based on a coded neighboring block of thechroma signals in accordance with a chroma intra prediction mode; and abitstream constructing unit 113 that, when the information relating tothe chroma intra prediction mode of the prediction block of chromasignals is coded, calculates syntax elements relating to chroma intraprediction modes including a mode in which the value of the chroma intraprediction mode is predicted based on the value of the luma intraprediction mode of the prediction block of the luma signals that islocated at the same position as the position of the prediction block ofchroma signals and constructs a bitstream by coding the syntax elementrelating to the luma intra prediction mode and the syntax elementrelating to the chroma intra prediction mode.

There is provided the picture coding device, wherein the bitstreamconstructing unit 113, when a chroma intra prediction mode is predictedbased on the luma intra prediction mode of the same position as theposition of the prediction block of chroma signals, sets the value ofthe luma intra prediction mode as the value of the chroma intraprediction mode in a case where the chroma format is 4:2:0 or 4:4:4.

There is provided the picture coding device, wherein the intraprediction unit 103, when a chroma intra prediction mode is predictedbased on the luma intra prediction mode located at the same position asthe position of the prediction block of chroma signals, uses an intraprediction direction derived by performing half-times scaling of theintra prediction direction of the luma intra prediction mode in thehorizontal direction or performing two-times scaling thereof in thevertical direction for the intra prediction of the chroma signal in acase where the chroma format is 4:2:2.

There is provided the picture coding device, wherein the bitstreamconstructing unit 113, when a chroma intra prediction mode is predictedbased on the luma intra prediction mode located at the same position asthe position of the prediction block of chroma signals, in a case wherethe chroma format is 4:2:2, sets the value of the intra prediction modecorresponding to an intra prediction direction derived by performing ½times scaling of the intra prediction direction of the luma intraprediction mode in the horizontal direction or performing two-timesscaling thereof in the vertical direction or the value of the intraprediction mode corresponding to an intra prediction direction close tothe intra prediction direction as the value of the chroma intraprediction mode.

As picture coding methods according to still another aspect of thepresent invention, there are the following methods.

There is provided a picture coding method for performing intraprediction coding of a picture signal including a luma signal and achroma signal in units of blocks and coding information relating to anintra prediction mode, the picture coding method including:

setting a prediction block of the luma signals and predicting a lumasignal based on a coded neighboring block of the luma signals inaccordance with the luma intra prediction mode when an intra predictionof the picture signal is made in units of prediction blocks;

setting a prediction block of chroma signals and predicting a chromasignal based on a coded neighboring block of the chroma signals inaccordance with the chroma intra prediction mode; and

calculating syntax elements relating to chroma intra prediction modesincluding a mode in which the value of the chroma intra prediction modeis predicted based on the value of the luma intra prediction mode of theprediction block of the luma signals that is located at the sameposition as the position of the prediction block of chroma signals andconstructing a bitstream by coding the syntax element relating to theluma intra prediction mode and the syntax element relating to the chromaintra prediction mode when the information relating to the chroma intraprediction mode of the prediction block of the chroma signals is coded.

There is provided the picture coding method, wherein, in the calculatingof syntax elements and the constructing of a bitstream, when a chromaintra prediction mode is predicted based on the luma intra predictionmode located at the same position as the position of the predictionblock of the chroma signals, in a case where the chroma format is 4:2:0or 4:4:4, the value of the luma intra prediction mode is set as thevalue of the chroma intra prediction mode.

There is provided the picture coding method, wherein, in the setting ofa prediction block and the predicting of a chroma signal, when a chromaintra prediction mode is predicted based on the luma intra predictionmode located at the same position as the position of the predictionblock of chroma signals, an intra prediction direction derived byperforming half-times scaling of the intra prediction direction of theluma intra prediction mode in the horizontal direction or performingtwo-times scaling thereof in the vertical direction is used for theintra prediction of the chroma signal in a case where the chroma formatis 4:2:2.

There is provided the picture coding method, wherein, in the calculatingof syntax elements and the constructing of a bitstream, when a chromaintra prediction mode is predicted based on the luma intra predictionmode located at the same position as the position of the predictionblock of chroma signals, in a case where the chroma format is 4:2:2, thevalue of the intra prediction mode corresponding to an intra predictiondirection derived by performing ½ times scaling of the intra predictiondirection of the luma intra prediction mode in the horizontal directionor performing two-times scaling thereof in the vertical direction or thevalue of the intra prediction mode corresponding to an intra predictiondirection close to the intra prediction direction is set as the value ofthe chroma intra prediction mode.

As picture decoding devices according to still another aspect of thepresent invention, there are following devices.

There is provided a picture decoding device that decodes informationrelating to an intra prediction mode and performs intra predictiondecoding of a picture signal including a luma signal and a chroma signalin units of blocks, the picture decoding device including:

a bitstream decoding unit 203 that decodes syntax elements relating to aluma intra prediction mode and a chroma intra prediction mode of aprediction block of chroma signals from a bitstream in which informationrelating to the luma intra prediction mode of a prediction block of theluma signals and information relating to the chroma intra predictionmode of a prediction block of chroma signals are coded, calculates thevalue of the luma intra prediction mode of the prediction block of theluma signals, and derives the value of the chroma intra prediction modeby predicting the value of the chroma intra prediction mode based on thevalue of the luma intra prediction mode of the prediction block of theluma signals that is located at the same position as the position of theprediction block of the chroma signals, when an intra prediction of thepicture signal is made in units of prediction blocks;

a luma signal intra prediction unit 206 that predicts a luma signalbased on a decoded neighboring block of the luma signals in accordancewith the luma intra prediction mode derived for each prediction block ofluma signals; and

a chroma signal intra prediction unit 206 that predicts a chroma signalbased on a decoded neighboring block of the chroma signals in accordancewith the chroma intra prediction mode derived for each prediction blockof the chroma signals.

There is provided the picture decoding device, wherein the bitstreamdecoding unit 203, when a chroma intra prediction mode is predictedbased on the luma intra prediction mode of the same position as theposition of the prediction block of chroma signals, sets the value ofthe luma intra prediction mode as the value of the chroma intraprediction mode in a case where the chroma format is 4:2:0 or 4:4:4.

There is provided the picture decoding device, wherein the chroma signalintra prediction unit 206, when a chroma intra prediction mode ispredicted based on the luma intra prediction mode located at the sameposition as the position of the prediction block of chroma signals, usesan intra prediction direction derived by performing half-times scalingof the intra prediction direction of the luma intra prediction mode inthe horizontal direction or performing two-times scaling thereof in thevertical direction for the intra prediction of the chroma signal in acase where the chroma format is 4:2:2.

There is provided the picture decoding device, wherein the bitstreamdecoding unit 203, when a chroma intra prediction mode is predictedbased on the luma intra prediction mode located at the same position asthe position of the prediction block of chroma signals, in a case wherethe chroma format is 4:2:2, sets the value of the intra prediction modecorresponding to an intra prediction direction derived by performing ½times scaling of the intra prediction direction of the luma intraprediction mode in the horizontal direction or performing two-timesscaling thereof in the vertical direction or the value of the intraprediction mode corresponding to an intra prediction direction close tothe intra prediction direction as the value of the chroma intraprediction mode.

As picture decoding methods according to the other aspects of thepresent invention, there are the following methods.

There is provided a picture decoding method for decoding informationrelating to an intra prediction mode and performing intra predictiondecoding of a picture signal including a luma signal and a chroma signalin units of blocks, the picture decoding method including:

decoding syntax elements relating to a luma intra prediction mode and achroma intra prediction mode of a prediction block of chroma signalsfrom a bitstream in which information relating to the luma intraprediction mode of a prediction block of the luma signals andinformation relating to the chroma intra prediction mode of a predictionblock of chroma signals are coded, calculating the value of the lumaintra prediction mode of the prediction block of the luma signals, andderiving the value of the chroma intra prediction mode by predicting thevalue of the chroma intra prediction mode based on the value of the lumaintra prediction mode of the prediction block of the luma signals thatis located at the same position as the position of the prediction blockof the chroma signals, when an intra prediction of the picture signal ismade in units of prediction blocks;

predicting a luma signal based on a decoded neighboring block of theluma signals in accordance with the luma intra prediction mode derivedfor each prediction block of luma signals; and

predicting a chroma signal based on a decoded neighboring block of thechroma signals in accordance with the chroma intra prediction modederived for each prediction block of the chroma signals.

There is provided the picture decoding method, wherein, in the decodingof syntax elements from a bitstream, when a chroma intra prediction modeis predicted based on the luma intra prediction mode of the sameposition as the position of the prediction block of chroma signals, thevalue of the luma intra prediction mode is set as the value of thechroma intra prediction mode in a case where the chroma format is 4:2:0or 4:4:4.

There is provided the picture decoding method, wherein, in thepredicting of a chroma signal, when a chroma intra prediction mode ispredicted based on the luma intra prediction mode located at the sameposition as the position of the prediction block of chroma signals, anintra prediction direction derived by performing half-times scaling ofthe intra prediction direction of the luma intra prediction mode in thehorizontal direction or performing two-times scaling thereof in thevertical direction is used for the intra prediction of the chroma signalin a case where the chroma format is 4:2:2.

There is provided the picture decoding method, wherein, in the decodingof syntax elements from a bitstream, when a chroma intra prediction modeis predicted based on the luma intra prediction mode located at the sameposition as the position of the prediction block of chroma signals, in acase where the chroma format is 4:2:2, the value of the intra predictionmode corresponding to an intra prediction direction derived byperforming ½ times scaling of the intra prediction direction of the lumaintra prediction mode in the horizontal direction or performingtwo-times scaling thereof in the vertical direction or the value of theintra prediction mode corresponding to an intra prediction directionclose to the intra prediction direction is set as the value of thechroma intra prediction mode.

A bitstream of a moving picture output by the picture coding deviceaccording to the embodiment described above has a specific data formatsuch that the bitstream can be decoded in accordance with the codingmethod used in the embodiment, and the picture decoding devicecorresponding to the picture coding device can decode the bitstreamhaving this specific data format.

In a case where a wired or wireless network is used so as to allow thebitstream to be transmitted and received between the picture codingdevice and the picture decoding device, the bitstream may be convertedto a data format that is appropriate to the transmission form of thetransmission path and be transmitted. In such a case, a picturetransmitting device that converts the bitstream output by the picturecoding device into coding data of a data format that is appropriate tothe transmission form of the transmission path and transmits the codingdata to the network and a picture receiving device that receives thecoding data from the network, restores a bitstream from the coding data,and supplies the restored bitstream to the picture decoding device aredisposed.

The picture transmitting device includes: a memory that buffers abitstream output by the picture coding device; a packet processing unitthat packetizes the bitstream; and a transmitting unit that transmitsthe packetized coding data through a network. The picture receivingdevice includes: a receiving unit that receives packetized coding datathrough a network; a memory that buffers the received coding data; and apacket processing unit that constructs a bitstream by performing apacket process of the coding data and supplies the bitstream to thepicture decoding device.

The above-described processes relating to coding and decoding may berealized not only as transmitting/storage/receiving devices usinghardware but also by firmware stored in a read only memory (ROM), aflash memory, or the like or software for a computer or the like. Thefirmware program and the software program may be provided with beingrecorded in a computer-readable recording medium, be provided from aserver through a wired or wireless network, or be provided as databroadcasting of a terrestrial or satellite digital broadcasts.

As above, the embodiment of the present invention has been described.However, the embodiment is merely an example, and it should beunderstood by those skilled in the art that various changes andmodifications may be made in each constituent element and thecombination of the processes, and such changes and modifications belongto the scope of the present invention.

[Item 1]

A picture coding device that performs intra prediction coding of apicture signal including a luma signal and a chroma signal in units ofblocks and codes information relating to an intra prediction mode, thepicture coding device including:

a luma signal intra prediction unit configured to set the first tofourth prediction blocks of luma signals acquired by partitioning theluma signals of a minimal coding block horizontally and vertically andpredict a luma signal based on a coded neighboring block of the lumasignals in accordance with a luma intra prediction mode for eachprediction block of the luma signals in a case where a partition mode inwhich the luma signals are partitioned horizontally and vertically isset when an intra prediction of the picture signal is made in units ofminimal coding blocks set in advance;

a chroma signal intra prediction unit configured to set a predictionblock of the chroma signals without partitioning the chroma signals ofthe minimal coding block and predict a chroma signal based on a codedneighboring block of the chroma signals in accordance with a chromaintra prediction mode in a case where the partition mode is set, and achroma format is 4:2:0; and

a bitstream constructing unit configured to code information relating tothe prediction mode of the minimal coding block and construct abitstream in which information relating to prediction modes is arrangedin order of, within the minimal coding block, the luma intra predictionmode of the first prediction block of luma signals, the luma intraprediction mode of the second prediction block of luma signals, the lumaintra prediction mode of the third prediction block of luma signals, theluma intra prediction mode of the fourth prediction block of lumasignals, and the chroma intra prediction mode of the prediction block ofthe chroma signals that is located at a reference position that is thesame as the position of the first prediction block of luma signals.

[Item 2]

The picture coding device described in Item 1, wherein the chroma signalintra prediction unit, in a mode for setting the chroma intra predictionmode in accordance with the luma intra prediction mode, sets the chromaintra prediction mode by using the value representing the luma intraprediction mode of a prediction block of first luma signals within aminimal coding block as the value representing the chroma intraprediction mode of a prediction block of chroma signals within theminimal coding block.

[Item 3]

A picture coding device that performs intra prediction coding of apicture signal including a luma signal and a chroma signal in units ofblocks and codes information relating to an intra prediction mode, thepicture coding device including:

a luma signal intra prediction unit that, when an intra prediction ofthe picture signal is made in units of minimal coding blocks set inadvance, in a case where a partition mode in which luma signals arepartitioned horizontally and vertically is set, sets the first to fourthprediction blocks of luma signals acquired by partitioning the lumasignals of a minimal coding block horizontally and vertically andpredicts a luma signal based on a coded neighboring block of the lumasignals in accordance with a luma intra prediction mode for eachprediction block of the luma signals;

a chroma signal intra prediction unit that, in a case where thepartition mode is set, and a chroma format is 4:4:4, sets the first tofourth prediction blocks of chroma signals acquired by partitioning thechroma signals of the minimal coding block horizontally and verticallyand predicts the chroma signal based on a coded neighboring block of thechroma signals in accordance with a chroma intra prediction mode foreach prediction block of the chroma signals; and

a bitstream constructing unit that codes information relating to theprediction mode of the minimal coding block and constructs a bitstreamin which information relating to the prediction modes is arranged inorder of, within the minimal coding block, the luma intra predictionmode of the first prediction block of luma signals, the luma intraprediction mode of the second prediction block of luma signals, the lumaintra prediction mode of the third prediction block of luma signals, theluma intra prediction mode of the fourth prediction block of lumasignals, the chroma intra prediction mode of the prediction block of thefirst chroma signals located at a reference position that is the same asthe position of the first prediction block of luma signals, the chromaintra prediction mode of the prediction block of the second chromasignals located at a reference position that is the same as the positionof the second prediction block of luma signals, the chroma intraprediction mode of the prediction block of the third chroma signalslocated at a reference position that is the same as the position of thethird prediction block of luma signals, and the chroma intra predictionmode of the prediction block of the fourth chroma signals located at areference position that is the same as the position of the fourthprediction block of luma signals.

[Item 4]

The picture coding device described in Item 3, wherein the chroma signalintra prediction unit, in a mode for setting the chroma intra predictionmode in accordance with the luma intra prediction mode, sets the chromaintra prediction modes of the prediction blocks of the first, second,third, and fourth chroma signals by using the values representing theluma intra prediction modes of the prediction blocks of the first,second, third, and fourth luma signals within a minimal coding block asthe values representing the chroma intra prediction modes of theprediction blocks of the first, second, third, and fourth chroma signalswithin the minimal coding block that are respectively located at samereference positions.

[Item 5]

A picture coding device that performs intra prediction coding of apicture signal including a luma signal and a chroma signal in units ofblocks and codes information relating to an intra prediction mode, thepicture coding device including:

a luma signal intra prediction unit that, when an intra prediction ofthe picture signal is made in units of minimal coding blocks set inadvance, in a case where a partition mode in which luma signals arepartitioned horizontally and vertically is set, sets the first to fourthprediction blocks of luma signals acquired by partitioning the lumasignals of a minimal coding block horizontally and vertically andpredicts a luma signal based on a coded neighboring block of the lumasignals in accordance with a luma intra prediction mode for eachprediction block of the luma signals;

a chroma signal intra prediction unit that, in a case where thepartition mode is set, and a chroma format is 4:2:2, sets predictionblocks of first and second chroma signals acquired by horizontallypartitioning the chroma signals of the minimal coding block and predictsthe chroma signal based on a coded neighboring block of chroma signalsin accordance with a chroma intra prediction mode for each predictionblock of the chroma signals; and

a bitstream constructing unit that codes information relating to theprediction mode of the minimal coding block and constructs a bitstreamin which information relating to the prediction modes is arranged inorder of, within the minimal coding block, the luma intra predictionmode of the first prediction block of luma signals, the luma intraprediction mode of the second prediction block of luma signals, the lumaintra prediction mode of the third prediction block of luma signals, theluma intra prediction mode of the fourth prediction block of lumasignals, the chroma intra prediction mode of the prediction block of thefirst chroma signals located at a reference position that is the same asthe position of the prediction block of the first luma signal, and thechroma intra prediction mode of the prediction block of the secondchroma signals located at a reference position that is the same as theposition of the third prediction block of luma signals.

[Item 6]

The picture coding device described in Item 5, wherein the chroma signalintra prediction unit, in a mode for setting the chroma intra predictionmode in accordance with the luma intra prediction mode, sets the chromaintra prediction modes of the prediction blocks of the first and secondchroma signals by converting the values representing the luma intraprediction modes of the prediction blocks of the first and third lumasignals within a minimal coding block into the values representing thechroma intra prediction modes of the prediction blocks of the first andsecond chroma signals within the minimal coding block that arerespectively located at same reference positions in accordance with aconversion rule set in advance.

[Item 7]

A picture coding method for performing intra prediction coding of apicture signal including a luma signal and a chroma signal in units ofblocks and coding information relating to an intra prediction mode, thepicture coding method including:

setting the first to fourth prediction blocks of luma signals acquiredby partitioning the luma signals of a minimal coding block horizontallyand vertically and predicting a luma signal based on a coded neighboringblock of the luma signals in accordance with a luma intra predictionmode for each prediction block of the luma signals when an intraprediction of the picture signal is made in units of minimal codingblocks set in advance, in a case where a partition mode in which theluma signals are partitioned horizontally and vertically is set;

setting a prediction block of chroma signals without partitioning thechroma signals of the minimal coding block and predicting a chromasignal based on a coded neighboring block of the chroma signals inaccordance with a chroma intra prediction mode in a case where thepartition mode is set, and a chroma format is 4:2:0; and

coding information relating to the prediction mode of the minimal codingblock and constructing a bitstream in which information relating to theprediction modes is arranged in order of, within the minimal codingblock, the luma intra prediction mode of the first prediction block ofluma signals, the luma intra prediction mode of the second predictionblock of luma signals, the luma intra prediction mode of the thirdprediction block of luma signals, the luma intra prediction mode of thefourth prediction block of luma signals, and the chroma intra predictionmode of the prediction block of the chroma signals located at areference position that is the same as the position of the firstprediction block of luma signals.

[Item 8]

A picture coding method for performing intra prediction coding of apicture signal including a luma signal and a chroma signal in units ofblocks and coding information relating to an intra prediction mode, thepicture coding method including:

setting the first to fourth prediction blocks of luma signals acquiredby partitioning the luma signals of a minimal coding block horizontallyand vertically and predicting a luma signal based on a coded neighboringblock of the luma signals in accordance with a luma intra predictionmode for each prediction block of the luma signals when an intraprediction of the picture signal is made in units of the minimal codingblocks set in advance, in a case where a partition mode in which theluma signals are partitioned horizontally and vertically is set;

setting the first to fourth prediction blocks of chroma signals acquiredby partitioning the chroma signals of the minimal coding blockhorizontally and vertically and predicting a chroma signal based on acoded neighboring block of the chroma signals in accordance with achroma intra prediction mode for each prediction block of the chromasignals in a case where the partition mode is set, and a chroma formatis 4:4:4; and

coding information relating to the prediction mode of the minimal codingblock and constructing a bitstream in which information relating to theprediction modes is arranged in order of, within the minimal codingblock, the luma intra prediction mode of the first prediction block ofluma signals, the luma intra prediction mode of the second predictionblock of luma signals, the luma intra prediction mode of the thirdprediction block of luma signals, the luma intra prediction mode of thefourth prediction block of luma signals, the chroma intra predictionmode of the prediction block of the first chroma signals located at areference position that is the same as the position of the firstprediction block of luma signals, the chroma intra prediction mode ofthe prediction block of the second chroma signals located at a referenceposition that is the same as the position of the second prediction blockof luma signals, the chroma intra prediction mode of the predictionblock of the third chroma signals located at a reference position thatis the same as the position of the third prediction block of lumasignals, and the chroma intra prediction mode of the prediction block ofthe fourth chroma signals located at a reference position that is thesame as the position of the fourth prediction block of luma signals.

[Item 9]

A picture coding method for performing intra prediction coding of apicture signal including a luma signal and a chroma signal in units ofblocks and coding information relating to an intra prediction mode, thepicture coding method including:

setting the first to fourth prediction blocks of luma signals acquiredby partitioning the luma signals of a minimal coding block horizontallyand vertically and predicting a luma signal based on a coded neighboringblock of the luma signals in accordance with a luma intra predictionmode for each prediction block of the luma signals when an intraprediction of the picture signal is made in units of the minimal codingblocks set in advance, in a case where a partition mode in which theluma signals are partitioned horizontally and vertically is set;

setting prediction blocks of first and second chroma signals acquired byhorizontally partitioning the chroma signals of the minimal coding blockand predicting a chroma signal based on a coded neighboring block of thechroma signals in accordance with a chroma intra prediction mode foreach prediction block of the chroma signals in a case where thepartition mode is set, and a chroma format is 4:2:2; and

coding information relating to the prediction mode of the minimal codingblock and constructing a bitstream in which information relating to theprediction modes is arranged in order of, within the minimal codingblock, the luma intra prediction mode of the first prediction block ofluma signals, the luma intra prediction mode of the second predictionblock of luma signals, the luma intra prediction mode of the thirdprediction block of luma signals, the luma intra prediction mode of thefourth prediction block of luma signals, the chroma intra predictionmode of the prediction block of the first chroma signals located at areference position that is the same as the position of the predictionblock of the first luma signal, and the chroma intra prediction mode ofthe prediction block of the second chroma signals located at a referenceposition that is the same as the position of the third prediction blockof luma signals.

[Item 10]

A picture coding program for performing intra prediction coding of apicture signal including a luma signal and a chroma signal in units ofblocks and coding information relating to an intra prediction mode, thepicture coding program causing a computer to perform:

setting the first to fourth prediction blocks of luma signals acquiredby partitioning the luma signals of a minimal coding block horizontallyand vertically and predicting a luma signal based on a coded neighboringblock of the luma signals in accordance with a luma intra predictionmode for each prediction block of the luma signals when an intraprediction of the picture signal is made in units of the minimal codingblocks set in advance, in a case where a partition mode in which theluma signals are partitioned horizontally and vertically is set;

setting a prediction block of the chroma signals without partitioningthe chroma signals of the minimal coding block and predicting a chromasignal based on a coded neighboring block of the chroma signals inaccordance with a chroma intra prediction mode in a case where thepartition mode is set, and a chroma format is 4:2:0; and

coding information relating to the prediction mode of the minimal codingblock and constructing a bitstream in which information relating to theprediction modes is arranged in order of, within the minimal codingblock, the luma intra prediction mode of the first prediction block ofluma signals, the luma intra prediction mode of the second predictionblock of luma signals, the luma intra prediction mode of the thirdprediction block of luma signals, the luma intra prediction mode of thefourth prediction block of luma signals, and the chroma intra predictionmode of the prediction block of the chroma signals located at areference position that is the same as the position of the firstprediction block of luma signals.

[Item 11]

A picture coding program for performing intra prediction coding of apicture signal including a luma signal and a chroma signal in units ofblocks and coding information relating to an intra prediction mode, thepicture coding program causing a computer to perform:

setting the first to fourth prediction blocks of luma signals acquiredby partitioning the luma signals of the minimal coding blockhorizontally and vertically and predicting a luma signal based on acoded neighboring block of luma signals in accordance with a luma intraprediction mode for each prediction block of the luma signals when anintra prediction of the picture signal is made in units of minimalcoding blocks set in advance, in a case where a partition mode in whichluma signals are partitioned horizontally and vertically is set;

setting the first to fourth prediction blocks of chroma signals acquiredby partitioning the chroma signals of the minimal coding blockhorizontally and vertically and predicting the chroma signal based on acoded neighboring block of the chroma signals in accordance with achroma intra prediction mode for each prediction block of the chromasignals in a case where the partition mode is set, and a chroma formatis 4:4:4; and

coding information relating to the prediction mode of the minimal codingblock and constructing a bitstream in which information relating to theprediction modes is arranged in order of, within the minimal codingblock, the luma intra prediction mode of the first prediction block ofluma signals, the luma intra prediction mode of the second predictionblock of luma signals, the luma intra prediction mode of the thirdprediction block of luma signals, the luma intra prediction mode of thefourth prediction block of luma signals, the chroma intra predictionmode of the prediction block of the first chroma signals located at areference position that is the same as the position of the firstprediction block of luma signals, the chroma intra prediction mode ofthe prediction block of the second chroma signals located at a referenceposition that is the same as the position of the second prediction blockof luma signals, the chroma intra prediction mode of the predictionblock of the third chroma signals located at a reference position thatis the same as the position of the third prediction block of lumasignals, and the chroma intra prediction mode of the prediction block ofthe fourth chroma signals located at a reference position that is thesame as the position of the fourth prediction block of luma signals.

[Item 12]

A picture coding program for performing intra prediction coding of apicture signal including a luma signal and a chroma signal in units ofblocks and coding information relating to an intra prediction mode, thepicture coding program causing a computer to perform:

setting the first to fourth prediction blocks of luma signals acquiredby partitioning the luma signals of the minimal coding blockhorizontally and vertically and predicting a luma signal based on acoded neighboring block of the luma signals in accordance with a lumaintra prediction mode for each prediction block of the luma signals whenan intra prediction of the picture signal is made in units of minimalcoding blocks set in advance, in a case where a partition mode in whichluma signals are partitioned horizontally and vertically is set;

setting prediction blocks of first and second chroma signals acquired byhorizontally partitioning the chroma signals of the minimal coding blockand predicting a chroma signal based on a coded neighboring block of thechroma signals in accordance with a chroma intra prediction mode foreach prediction block of the chroma signals in a case where thepartition mode is set, and a chroma format is 4:2:2; and

coding information relating to the prediction mode of the minimal codingblock and constructing a bitstream in which information relating to theprediction modes is arranged in order of, within the minimal codingblock, the luma intra prediction mode of the first prediction block ofluma signals, the luma intra prediction mode of the second predictionblock of luma signals, the luma intra prediction mode of the thirdprediction block of luma signals, the luma intra prediction mode of thefourth prediction block of luma signals, the chroma intra predictionmode of the prediction block of the first chroma signals located at areference position that is the same as the position of the firstprediction block of luma signals, and the chroma intra prediction modeof the prediction block of the second chroma signals located at areference position that is the same as the position of the thirdprediction block of luma signals.

[Item 13]

A picture decoding device that decodes information relating to an intraprediction mode and performs intra prediction decoding of a picturesignal including a luma signal and a chroma signal in units of blocks,the picture decoding device including:

a bitstream decoding unit configured to decode information relating to aluma intra prediction mode of a prediction block of luma signals andinformation relating to a chroma intra prediction mode of the predictionblock of chroma signals in the order of arrangement from a bitstream inwhich coding information relating to the prediction mode is arranged inorder of, within a minimal decoding block, a luma intra prediction modeof the first prediction block of luma signals, a luma intra predictionmode of the second prediction block of luma signals, a luma intraprediction mode of the third prediction block of luma signals, a lumaintra prediction mode of the fourth prediction block of luma signals,and a chroma intra prediction mode of the prediction block of the chromasignals that is located at a reference position that is the same as theposition of the first prediction block of luma signals, in a case wherea partition mode in which the luma signals are partitioned horizontallyand vertically is derived and a chroma format is 4:2:0 when an intraprediction of the picture signal is made in units of minimal decodingblocks set in advance;

a luma signal intra prediction unit that, in a case where the partitionmode is set, is configured to set the first to fourth prediction blocksof luma signals acquired by partitioning the luma signals of the minimaldecoding block horizontally and vertically and predict a luma signalbased on a decoded neighboring block of the luma signals in accordancewith each luma intra prediction mode derived based on the informationrelating to the luma intra prediction mode for each decoded predictionblock of the luma signals; and

a chroma signal intra prediction unit configured to set the predictionblock of the chroma signals without partitioning the chroma signals ofthe minimal decoding block and predict a chroma signal based on adecoded neighboring block of the chroma signals in accordance with achroma intra prediction mode derived based on the information relatingto the decoded chroma intra prediction mode in a case where thepartition mode is set, and the chroma format is 4:2:0.

[Item 14]

The picture decoding device described in Item 13, wherein the chromasignal intra prediction unit, in a mode for setting the chroma intraprediction mode in accordance with the luma intra prediction mode, setsthe chroma intra prediction mode by using the value representing theluma intra prediction mode of a prediction block of first luma signalswithin the minimal decoding block as the value representing the chromaintra prediction mode of a prediction block of chroma signals within theminimal decoding block.

[Item 15]

A picture decoding device that decodes information relating to an intraprediction mode and performs intra prediction decoding of a picturesignal including a luma signal and a chroma signal in units of blocks,the picture decoding device including:

a bitstream decoding unit that decodes information relating to a lumaintra prediction mode of the prediction block of luma signals andinformation relating to a chroma intra prediction mode of the predictionblock of chroma signals in the order of arrangement from a bitstream inwhich coding information relating to the prediction mode is arranged inorder of, within the minimal decoding block, a luma intra predictionmode of the first prediction block of luma signals, a luma intraprediction mode of the second prediction block of luma signals, a lumaintra prediction mode of the third prediction block of luma signals, aluma intra prediction mode of the fourth prediction block of lumasignals, a chroma intra prediction mode of the prediction block of thefirst chroma signals located at a reference position that is the same asthe position of the first prediction block of luma signals, a chromaintra prediction mode of the prediction block of the second chromasignals located at a reference position that is the same as the positionof the second prediction block of luma signals, a chroma intraprediction mode of the prediction block of the third chroma signalslocated at a reference position that is the same as the position of thethird prediction block of luma signals, and a chroma intra predictionmode of the prediction block of the fourth chroma signals located at areference position that is the same as the position of the fourthprediction block of luma signals, in a case where a partition mode inwhich the luma signals are partitioned horizontally and vertically isderived, and a chroma format is 4:4:4 when an intra prediction of apicture signal is made in units of minimal decoding blocks set inadvance;

a luma signal intra prediction unit that sets the first to fourthprediction blocks of luma signals acquired by partitioning the lumasignals of the minimal decoding block horizontally and vertically andpredicts the luma signal based on the decoded neighboring block of lumasignals in accordance with each luma intra prediction mode derived basedon the information relating to the luma intra prediction mode for eachdecoded prediction block of the luma signals in a case where thepartition mode is set; and

a chroma signal intra prediction unit that sets the first to fourthprediction blocks of chroma signals that are acquired by partitioningthe chroma signals of the minimal decoding block horizontally andvertically and predicts the chroma signal based on a decoded neighboringblock of chroma signals in accordance with a chroma intra predictionmode derived based on the information relating to the chroma intraprediction mode for each decoded prediction block of the chroma signalsin a case where the partition mode is set, and the chroma format is4:4:4.

[Item 16]

The picture decoding device described in Item 15, wherein the chromasignal intra prediction unit, in a mode for setting the chroma intraprediction mode in accordance with the luma intra prediction mode, setsthe chroma intra prediction modes of the prediction blocks of the first,second, third, and fourth chroma signals by using the valuesrepresenting the luma intra prediction modes of the prediction blocks ofthe first, second, third, and fourth luma signals within the minimaldecoding block as the values representing the chroma intra predictionmodes of the prediction blocks of the first, second, third, and fourthchroma signals within the minimal decoding block that are respectivelylocated at same reference positions.

[Item 17]

A picture decoding device that decodes information relating to an intraprediction mode and performs intra prediction decoding of a picturesignal including a luma signal and a chroma signal in units of blocks,the picture decoding device including:

a bitstream decoding unit that decodes information relating to a lumaintra prediction mode of the prediction block of luma signals andinformation relating to a chroma intra prediction mode of the predictionblock of chroma signals in order of arrangement from a bitstream inwhich coding information relating to the prediction mode is arranged inthe order of, within the minimal decoding block, the luma intraprediction mode of the first prediction block of luma signals, the lumaintra prediction mode of the second prediction block of luma signals,the luma intra prediction mode of the third prediction block of lumasignals, the luma intra prediction mode of the fourth prediction blockof luma signals, the chroma intra prediction mode of the predictionblock of the first chroma signals located at a reference position thatis the same as the position of the prediction block of the first lumasignal, and the chroma intra prediction mode of the prediction block ofthe second chroma signals located at a reference position that is thesame as the position of the third prediction block of luma signals in acase where a partition mode in which the luma signals are horizontallyand vertically partitioned is derived, and a chroma format is 4:2:2 whenan intra prediction of a picture signal is made in units of minimaldecoding blocks set in advance;

a luma signal intra prediction unit that, in a case where the partitionmode is set, sets the first to fourth prediction blocks of luma signalsacquired by partitioning the luma signals of the minimal decoding blockhorizontally and vertically and predicts the luma signal based on thedecoded neighboring block of luma signals in accordance with each lumaintra prediction mode derived based on the information relating to theluma intra prediction mode for each decoded prediction block of the lumasignals; and

a chroma signal intra prediction unit that, in a case where thepartition mode is set, and the chroma format is 4:2:2, sets predictionblocks of first and second chroma signals that are acquired byhorizontally partitioning the chroma signals of the minimal decodingblock and predicts the chroma signal based on a decoded neighboringblock of chroma signals in accordance with a chroma intra predictionmode derived based on the information relating to the chroma intraprediction mode for each decoded prediction block of the chroma signals.

[Item 18]

The picture decoding device described in Item 17, wherein the chromasignal intra prediction unit, in a mode for setting the chroma intraprediction mode in accordance with the luma intra prediction mode, setsthe chroma intra prediction modes of the prediction blocks of the firstand second chroma signals by converting the values representing the lumaintra prediction modes of the prediction blocks of the first and thirdluma signals within the minimal decoding block into the valuesrepresenting the chroma intra prediction modes of the prediction blocksof the first and second chroma signals within the minimal decoding blockthat are respectively located at same reference positions in accordancewith a conversion rule set in advance.

[Item 19]

A picture decoding method for decoding information relating to an intraprediction mode and performing intra prediction decoding of a picturesignal including a luma signal and a chroma signal in units of blocks,the picture decoding method including:

decoding information relating to a luma intra prediction mode of theprediction block of luma signals and information relating to a chromaintra prediction mode of the prediction block of chroma signals in theorder of arrangement from a bitstream in which coding informationrelating to the prediction mode is arranged in order of, within theminimal decoding block, a luma intra prediction mode of the firstprediction block of luma signals, a luma intra prediction mode of thesecond prediction block of luma signals, a luma intra prediction mode ofthe third prediction block of luma signals, a luma intra prediction modeof the fourth prediction block of luma signals, and a chroma intraprediction mode of the prediction block of the chroma signals that islocated at a reference position that is the same as the position of thefirst prediction block of luma signals in a case where a partition modein which the luma signals are partitioned horizontally and vertically isderived and a chroma format is 4:2:0 when an intra prediction of apicture signal is made in units of minimal decoding blocks set inadvance;

setting the first to fourth prediction blocks of luma signals acquiredby partitioning the luma signals of the minimal decoding blockhorizontally and vertically and predicting a luma signal based on adecoded neighboring block of the luma signals in accordance with eachluma intra prediction mode derived based on the information relating tothe luma intra prediction mode for each decoded prediction block of theluma signals in a case where the partition mode is set; and

setting the prediction block of the chroma signals without partitioningthe chroma signals of the minimal decoding block and predicting a chromasignal based on a decoded neighboring block of the chroma signals inaccordance with a chroma intra prediction mode derived based on theinformation relating to the decoded chroma intra prediction mode in acase where the partition mode is set, and the chroma format is 4:2:0.

[Item 20]

A picture decoding method for decoding information relating to an intraprediction mode and performing intra prediction decoding of a picturesignal including a luma signal and a chroma signal in units of blocks,the picture decoding method including:

decoding information relating to a luma intra prediction mode of aprediction block of the luma signals and information relating to achroma intra prediction mode of the prediction block of the chromasignals in the order of arrangement from a bitstream in which codinginformation relating to a prediction mode is arranged in order of,within a minimal decoding block, a luma intra prediction mode of aprediction block of first luma signals, a luma intra prediction mode ofa prediction block of second luma signals, a luma intra prediction modeof a prediction block of third luma signals, a luma intra predictionmode of a prediction block of fourth luma signals, a chroma intraprediction mode of a prediction block of first chroma signals located ata reference position that is the same as the position of the firstprediction block of luma signals, a chroma intra prediction mode of aprediction block of second chroma signals located at a referenceposition that is the same as the position of the second prediction blockof luma signals, a chroma intra prediction mode of a prediction block ofthird chroma signals located at a reference position that is the same asthe position of the third prediction block of luma signals, and a chromaintra prediction mode of a prediction block of fourth chroma signalslocated at a reference position that is the same as the position of thefourth prediction block of luma signals, in a case where a partitionmode in which the luma signals are partitioned horizontally andvertically is derived, and a chroma format is 4:4:4 when an intraprediction of the picture signal is made in units of the minimaldecoding blocks set in advance;

setting the first to fourth prediction blocks of luma signals acquiredby partitioning the luma signals of the minimal decoding blockhorizontally and vertically and predicting a luma signal based on adecoded neighboring block of the luma signals in accordance with eachluma intra prediction mode derived based on the information relating tothe luma intra prediction mode for each decoded prediction block of theluma signals in a case where the partition mode is set; and

setting the first to fourth prediction blocks of chroma signals that areacquired by partitioning the chroma signals of the minimal decodingblock horizontally and vertically and predicting a chroma signal basedon a decoded neighboring block of the chroma signals in accordance witheach chroma intra prediction mode derived based on the informationrelating to the chroma intra prediction mode for each decoded predictionblock of the chroma signals in a case where the partition mode is set,and the chroma format is 4:4:4.

[Item 21]

A picture decoding method for decoding information relating to an intraprediction mode and performing intra prediction decoding of a picturesignal including a luma signal and a chroma signal in units of blocks,the picture decoding method including:

decoding information relating to a luma intra prediction mode of aprediction block of the luma signals and information relating to achroma intra prediction mode of a prediction block of the chroma signalsin the order of arrangement from a bitstream in which coding informationrelating to a prediction mode is arranged in order of, within a minimaldecoding block, the luma intra prediction mode of a prediction block offirst luma signals, the luma intra prediction mode of a prediction blockof second luma signals, the luma intra prediction mode of a predictionblock of third luma signals, the luma intra prediction mode of aprediction block of fourth luma signals, the chroma intra predictionmode of a prediction block of first chroma signals located at areference position that is the same as the position of the predictionblock of the first luma signal, and the chroma intra prediction mode ofa prediction block of second chroma signals located at a referenceposition that is the same as the position of the third prediction blockof luma signals in a case where a partition mode in which the lumasignals are partitioned horizontally and vertically is derived, and achroma format is 4:2:2 when an intra prediction of the picture signal ismade in units of the minimal decoding blocks set in advance;

setting the first to fourth prediction blocks of luma signals acquiredby partitioning the luma signals of the minimal decoding blockhorizontally and vertically and predicting a luma signal based on adecoded neighboring block of the luma signals in accordance with eachluma intra prediction mode derived based on the information relating tothe luma intra prediction mode for each decoded prediction block of theluma signals in a case where the partition mode is set; and

setting the prediction blocks of the first and second chroma signalsthat are acquired by horizontally partitioning the chroma signals of theminimal decoding block and predicting a chroma signal based on a decodedneighboring block of the chroma signals in accordance with each chromaintra prediction mode derived based on the information relating to thechroma intra prediction mode for each decoded prediction block of thechroma signals in a case where the partition mode is set, and the chromaformat is 4:2:2.

[Item 22]

A picture decoding program for decoding information relating to an intraprediction mode and performing intra prediction decoding of a picturesignal including a luma signal and a chroma signal in units of blocks,the picture decoding program causing a computer to perform:

decoding information relating to a luma intra prediction mode of aprediction block of the luma signals and information relating to achroma intra prediction mode of a prediction block of the chroma signalsin the order of arrangement from a bitstream in which coding informationrelating to a prediction mode is arranged in order of, within a minimaldecoding block, a luma intra prediction mode of a prediction block offirst luma signals, a luma intra prediction mode of a prediction blockof second luma signals, a luma intra prediction mode of a predictionblock of third luma signals, a luma intra prediction mode of aprediction block of fourth luma signals, and a chroma intra predictionmode of a prediction block of the chroma signals that is located at areference position that is the same as the position of the firstprediction block of luma signals in a case where a partition mode inwhich the luma signals are partitioned horizontally and vertically isderived and a chroma format is 4:2:0 when an intra prediction of thepicture signal is made in units of the minimal decoding blocks set inadvance;

setting the first to fourth prediction blocks of luma signals acquiredby partitioning the luma signals of the minimal decoding blockhorizontally and vertically and predicting a luma signal based on adecoded neighboring block of the luma signals in accordance with eachluma intra prediction mode derived based on the information relating tothe luma intra prediction mode for each decoded prediction block of theluma signals in a case where the partition mode is set; and

setting the prediction block of the chroma signals without partitioningthe chroma signals of the minimal decoding block and predicting a chromasignal based on a decoded neighboring block of the chroma signals inaccordance with the chroma intra prediction mode derived based on theinformation relating to the decoded chroma intra prediction mode in acase where the partition mode is set, and the chroma format is 4:2:0.

[Item 23]

A picture decoding program for decoding information relating to an intraprediction mode and performing intra prediction decoding of a picturesignal including a luma signal and a chroma signal in units of blocks,the picture decoding program causing a computer to perform:

decoding information relating to a luma intra prediction mode of aprediction block of the luma signals and information relating to achroma intra prediction mode of a prediction block of the chroma signalsin the order of arrangement from a bitstream in which coding informationrelating to a prediction mode is arranged in order of, within a minimaldecoding block, a luma intra prediction mode of a prediction block offirst luma signals, a luma intra prediction mode of a prediction blockof second luma signals, a luma intra prediction mode of a predictionblock of third luma signals, a luma intra prediction mode of aprediction block of fourth luma signals, a chroma intra prediction modeof a prediction block of first chroma signals located at a referenceposition that is the same as the position of the first prediction blockof luma signals, a chroma intra prediction mode of a prediction block ofsecond chroma signals located at a reference position that is the sameas the position of the second prediction block of luma signals, a chromaintra prediction mode of a prediction block of third chroma signalslocated at a reference position that is the same as the position of thethird prediction block of luma signals, and a chroma intra predictionmode of a prediction block of fourth chroma signals located at areference position that is the same as the position of the fourthprediction block of luma signals, in a case where a partition mode inwhich the luma signals are partitioned horizontally and vertically isderived, and a chroma format is 4:4:4 when an intra prediction of apicture signal is made in units of the minimal decoding blocks set inadvance;

setting the first to fourth prediction blocks of luma signals acquiredby partitioning the luma signals of the minimal decoding blockhorizontally and vertically and predicting a luma signal based on adecoded neighboring block of the luma signals in accordance with eachluma intra prediction mode derived based on the information relating tothe luma intra prediction mode for each decoded prediction block of theluma signals in a case where the partition mode is set; and

setting the first to fourth prediction blocks of chroma signals that areacquired by partitioning the chroma signals of the minimal decodingblock horizontally and vertically and predicting a chroma signal basedon a decoded neighboring block of the chroma signals in accordance witheach chroma intra prediction mode derived based on the informationrelating to the chroma intra prediction mode for each decoded predictionblock of the chroma signals in a case where the partition mode is set,and the chroma format is 4:4:4.

[Item 24]

A picture decoding program for decoding information relating to an intraprediction mode and performing intra prediction decoding of a picturesignal including a luma signal and a chroma signal in units of blocks,the picture decoding program causing a computer to perform:

decoding information relating to a luma intra prediction mode of aprediction block of the luma signals and information relating to achroma intra prediction mode of a prediction block of the chroma signalsin the order of arrangement from a bitstream in which coding informationrelating to a prediction mode is arranged in order of, within a minimaldecoding block, the luma intra prediction mode of a prediction block offirst luma signals, the luma intra prediction mode of a prediction blockof second luma signals, the luma intra prediction mode of a predictionblock of third luma signals, the luma intra prediction mode of aprediction block of fourth luma signals, the chroma intra predictionmode of a prediction block of first chroma signals located at areference position that is the same as the position of the predictionblock of the first luma signal, and the chroma intra prediction mode ofa prediction block of second chroma signals located at a referenceposition that is the same as the position of the third prediction blockof luma signals in a case where a partition mode in which the lumasignals are partitioned horizontally and vertically is derived, and achroma format is 4:2:2 when an intra prediction of a picture signal ismade in units of the minimal decoding blocks set in advance;

setting the first to fourth prediction blocks of luma signals acquiredby partitioning the luma signals of the minimal decoding blockhorizontally and vertically and predicting a luma signal based on adecoded neighboring block of the luma signals in accordance with eachluma intra prediction mode derived based on the information relating tothe luma intra prediction mode for each decoded prediction block of theluma signals in a case where the partition mode is set; and

setting the prediction blocks of the first and second chroma signalsthat are acquired by horizontally partitioning the chroma signals of theminimal decoding block and predicting a chroma signal based on a decodedneighboring block of the chroma signals in accordance with each chromaintra prediction mode derived based on the information relating to thechroma intra prediction mode for each decoded prediction block of thechroma signals in a case where the partition mode is set, and the chromaformat is 4:2:2.

What is claimed is:
 1. A picture coding device that performs intraprediction coding of a picture signal including a luma signal and achroma signal in units of blocks and codes information relating to anintra prediction mode, the picture coding device comprising: an intraprediction unit configured to derive a value of a chroma intraprediction mode from a conversion table representing a value of thechroma intra prediction mode having a chroma format of 4:2:2 based on avalue of a luma intra prediction mode of a prediction block located at asame position as the position of a prediction block of the chroma signalin a case where the chroma format is 4:2:2 and derive a value of thechroma intra prediction mode based on a value of the luma intraprediction mode of a prediction block located at a same position as theposition of a prediction block of the chroma signal without using theconversion table in a case where the chroma format is not 4:2:2, whereinthe conversion table shows at least values representing a plurality ofchroma intra prediction modes having prediction directions that arerespectively closest to a plurality of directions derived by performing½ times scaling horizontally for prediction directions of a plurality ofthe luma intra prediction modes in which reference destinations arehorizontally aligned and the conversion table shows a same unalteredvalue as a value representing the chroma intra prediction mode as to avalue representing the luma intra prediction mode of vertical predictionin which a prediction direction is a vertical direction, wherein theintra prediction unit is implemented using hardware, memory storingfirmware, or a computer with software.
 2. A picture coding method forperforming intra prediction coding of a picture signal including a lumasignal and a chroma signal in units of blocks and coding informationrelating to an intra prediction mode, the picture coding methodcomprising: an intra prediction step of deriving a value of a chromaintra prediction mode from a conversion table representing a value ofthe chroma intra prediction mode having a chroma format of 4:2:2 basedon a value of a luma intra prediction mode of a prediction block locatedat a same position as the position of a prediction block of the chromasignal in a case where the chroma format is 4:2:2 and deriving a valueof the chroma intra prediction mode based on a value of the luma intraprediction mode of a prediction block located at a same position as theposition of a prediction block of the chroma signal without using theconversion table in a case where the chroma format is not 4:2:2, whereinthe conversion table shows at least values representing a plurality ofchroma intra prediction modes having prediction directions that arerespectively closest to a plurality of directions derived by performing½ times scaling horizontally for prediction directions of a plurality ofthe luma intra prediction modes in which reference destinations arehorizontally aligned and the conversion table shows a same unalteredvalue as a value representing the chroma intra prediction mode as to avalue representing the luma intra prediction mode of vertical predictionin which a prediction direction is a vertical direction, wherein theintra prediction step is performed using hardware, memory storingfirmware, or a computer with software.
 3. A non-transitorycomputer-readable recording medium having embodied thereon a picturecoding program for performing intra prediction coding of a picturesignal including a luma signal and a chroma signal in units of blocksand coding information relating to an intra prediction mode, the picturecoding program causing a computer to execute: an intra prediction stepof deriving a value of a chroma intra prediction mode from a conversiontable representing a value of the chroma intra prediction mode having achroma format of 4:2:2 based on a value of a luma intra prediction modeof a prediction block located at a same position as the position of aprediction block of the chroma signal in a case where the chroma formatis 4:2:2 and deriving a value of the chroma intra prediction mode basedon a value of the luma intra prediction mode of a prediction blocklocated at a same position as the position of a prediction block of thechroma signal without using the conversion table in a case where thechroma format is not 4:2:2, wherein the conversion table shows at leastvalues representing a plurality of chroma intra prediction modes havingprediction directions that are respectively closest to a plurality ofdirections derived by performing ½ times scaling horizontally forprediction directions of a plurality of the luma intra prediction modesin which reference destinations are horizontally aligned and theconversion table shows a same unaltered value as a value representingthe chroma intra prediction mode as to a value representing the lumaintra prediction mode of vertical prediction in which a predictiondirection is a vertical direction.